Nether Portal laggy

Please force a crash by pressing F3 + C for 10 seconds while in-game and attach the crash report ([minecraft/crash-reports/crash-<DATE>-client.txt|http://hopper.minecraft.net/help/finding-minecraft-data-folder]) here.

Minecraft Crash Report ----
// Ouch. That hurt 😞

Time: 1/29/14 7:27 AM
Description: Manually triggered debug crash

java.lang.Throwable
at bby.p(SourceFile:1437)
at bby.aj(SourceFile:774)
at bby.f(SourceFile:728)
at net.minecraft.client.main.Main.main(SourceFile:154)

A detailed walkthrough of the error, its code path and all known details is as follows:
---------------------------------------------------------------------------------------

– Head –
Stacktrace:
at bmw.a(SourceFile:298)

– Affected level –
Details:
Level name: MpServer
All players: 1 total; [boy['snackyzac'/34677, l='MpServer', x=10.00, y=54.62, z=-88.00]]
Chunk stats: MultiplayerChunkCache: 289, 289
Level seed: 0
Level generator: ID 00 - default, ver 1. Features enabled: false
Level generator options:
Level spawn location: 8.00,64.00,8.00 - World: (8,64,8), Chunk: (at 8,4,8 in 0,0; contains blocks 0,0,0 to 15,255,15), Region: (0,0; contains chunks 0,0 to 31,31, blocks 0,0,0 to 511,255,511)
Level time: 9163336 game time, 9717999 day time
Level dimension: 0
Level storage version: 0x00000 - Unknown?
Level weather: Rain time: 0 (now: false), thunder time: 0 (now: false)
Level game mode: Game mode: survival (ID 0). Hardcore: false. Cheats: false
Forced entities: 55 total; [sm['Experience Orb'/68617, l='MpServer', x=69.56, y=59.25, z=-91.69], yi['Zombie Pigman'/68601, l='MpServer', x=4.38, y=66.00, z=-84.84], yg['Magma Cube'/68616, l='MpServer', x=67.31, y=21.00, z=-83.69], yi['Zombie Pigman'/68600, l='MpServer', x=10.03, y=66.00, z=-85.30], yi['Zombie Pigman'/68619, l='MpServer', x=65.69, y=58.00, z=-79.91], sm['Experience Orb'/68618, l='MpServer', x=78.03, y=65.25, z=-93.47], yi['Zombie Pigman'/68602, l='MpServer', x=4.53, y=66.00, z=-88.34], yi['Zombie Pigman'/68605, l='MpServer', x=41.30, y=95.00, z=-38.53], yi['Zombie Pigman'/68621, l='MpServer', x=73.84, y=75.00, z=-51.94], ym['Skeleton'/68604, l='MpServer', x=32.91, y=80.00, z=-104.56], yi['Zombie Pigman'/68620, l='MpServer', x=65.75, y=58.00, z=-62.88], yi['Zombie Pigman'/68607, l='MpServer', x=61.91, y=58.00, z=-80.53], zm['arrow'/68606, l='MpServer', x=58.03, y=75.63, z=-112.91], yg['Magma Cube'/68609, l='MpServer', x=63.69, y=54.00, z=-49.94], yi['Zombie Pigman'/68593, l='MpServer', x=-25.75, y=54.00, z=-23.13], yg['Magma Cube'/68608, l='MpServer', x=58.88, y=53.00, z=-85.34], yg['Magma Cube'/68611, l='MpServer', x=74.45, y=25.00, z=-135.26], yi['Zombie Pigman'/68594, l='MpServer', x=-12.34, y=58.00, z=-165.47], yi['Zombie Pigman'/68610, l='MpServer', x=63.47, y=58.00, z=-63.66], ym['Skeleton'/68613, l='MpServer', x=74.22, y=68.00, z=-118.13], xy['Blaze'/68597, l='MpServer', x=-5.50, y=61.00, z=-83.28], ym['Skeleton'/68612, l='MpServer', x=73.00, y=67.00, z=-117.25], yg['Magma Cube'/68615, l='MpServer', x=73.78, y=22.00, z=-88.69], yi['Zombie Pigman'/68599, l='MpServer', x=3.41, y=66.00, z=-84.88], yg['Magma Cube'/68614, l='MpServer', x=67.31, y=20.00, z=-80.31], xy['Blaze'/68598, l='MpServer', x=-6.22, y=61.00, z=-79.94], yi['Zombie Pigman'/68588, l='MpServer', x=-32.50, y=53.00, z=-30.50], yi['Zombie Pigman'/68589, l='MpServer', x=-37.38, y=54.00, z=-31.53], yi['Zombie Pigman'/68590, l='MpServer', x=-32.69, y=54.00, z=-29.25], yi['Zombie Pigman'/68576, l='MpServer', x=-56.56, y=78.00, z=-128.06], yi['Zombie Pigman'/68577, l='MpServer', x=-62.72, y=78.00, z=-104.84], yi['Zombie Pigman'/68625, l='MpServer', x=89.50, y=89.00, z=-49.50], yi['Zombie Pigman'/68578, l='MpServer', x=-51.16, y=75.00, z=-17.00], yi['Zombie Pigman'/68626, l='MpServer', x=89.03, y=89.00, z=-48.47], yi['Zombie Pigman'/68627, l='MpServer', x=79.09, y=92.00, z=-38.25], wf['Chicken'/68579, l='MpServer', x=-58.83, y=74.00, z=-17.53], yi['Zombie Pigman'/68580, l='MpServer', x=-57.47, y=74.00, z=-10.91], sm['Experience Orb'/68629, l='MpServer', x=96.97, y=32.25, z=-163.41], yi['Zombie Pigman'/68581, l='MpServer', x=-53.28, y=73.00, z=-9.60], yi['Zombie Pigman'/68583, l='MpServer', x=-54.76, y=73.00, z=-12.00], yi['Zombie Pigman'/68571, l='MpServer', x=-66.13, y=78.00, z=-120.09], yi['Zombie Pigman'/68570, l='MpServer', x=-65.00, y=79.00, z=-127.66], zs['Small Fireball'/68575, l='MpServer', x=-53.38, y=89.25, z=-134.88], yi['Zombie Pigman'/68574, l='MpServer', x=-51.31, y=76.00, z=-128.41], sm['Experience Orb'/68653, l='MpServer', x=142.91, y=39.25, z=-143.94], yi['Zombie Pigman'/68572, l='MpServer', x=-68.44, y=79.00, z=-107.26], boy['snackyzac'/34677, l='MpServer', x=10.00, y=54.62, z=-88.00], yi['Zombie Pigman'/68666, l='MpServer', x=50.66, y=74.00, z=-75.72], yi['Zombie Pigman'/68667, l='MpServer', x=87.66, y=94.00, z=-35.59], xy['Blaze'/68665, l='MpServer', x=57.50, y=74.00, z=-67.50], yi['Zombie Pigman'/68670, l='MpServer', x=79.91, y=91.00, z=-42.03], yi['Zombie Pigman'/68669, l='MpServer', x=86.50, y=93.00, z=-38.50], yi['Zombie Pigman'/68662, l='MpServer', x=-57.25, y=63.00, z=-32.72], yi['Zombie Pigman'/68663, l='MpServer', x=-54.00, y=61.57, z=-32.46], ye['Ghast'/68661, l='MpServer', x=-45.83, y=90.16, z=-14.89]]
Retry entities: 0 total; []
Server brand: vanilla
Server type: Integrated singleplayer server
Stacktrace:
at bmw.a(SourceFile:298)
at bby.b(SourceFile:2029)
at bby.f(SourceFile:737)
at net.minecraft.client.main.Main.main(SourceFile:154)

– System Details –
Details:
Minecraft Version: 14w04b
Operating System: Windows 8 (x86) version 6.2
Java Version: 1.7.0_51, Oracle Corporation
Java VM Version: Java HotSpot(TM) Client VM (mixed mode), Oracle Corporation
Memory: 169852192 bytes (161 MB) / 376102912 bytes (358 MB) up to 518979584 bytes (494 MB)
JVM Flags: 2 total; -XX:HeapDumpPath=MojangTricksIntelDriversForPerformance_javaw.exe_minecraft.exe.heapdump -Xmx512M
IntCache: cache: 0, tcache: 30, allocated: 12, tallocated: 94
Launched Version: 14w04b
LWJGL: 2.9.1
OpenGL: AMD Radeon HD 8550G GL version 4.2.12422 Compatibility Profile Context 13.152.0.0, ATI Technologies Inc.
GL Caps: Using GL 1.3 multitexturing.
Using framebuffer objects because OpenGL 3.0 is supported and separate blending is supported.
Anisotropic filtering is supported and maximum anisotropy is 16.
Shaders are available because OpenGL 2.1 is supported.

Is Modded: Probably not. Jar signature remains and client brand is untouched.
Type: Client (map_client.txt)
Resource Packs: []
Current Language: English (US)
Profiler Position: N/A (disabled)
Anisotropic Filtering: Off (1)

I would like to add that it isn't the same amount once I go back through into the overworld from the nether it is much less.

Update your graphics driver to Catalyst 13.12: http://support.amd.com/en-us/download/desktop?os=Windows+7+-+32