I'm having huge FPS(dipping to 1-2 FPS...rarely getting above 10 FPS) problems with 13w41b as well. I have an Intel HD2000 chipset and wondered if the "fix" for the Intel chipsets had been broken. Even 1.6.4 is running badly. I can launch 1.5.2 with the old .exe and it seems to run fine. 20-25FPS.
Looks like my report(MC-36105) was classified a duplicate of this one, but I'm not sure that it is the same problem as this one.
What I can report is that with Intel Integrated graphics(HD2000 in my case), Full screen mode now causes terrible performance(unplayable 3-10FPS). When you hit F11 to go to "Windowed" mode, the performance comes back and is playable(20-24 FPS). Even when maximized, the performance is much better than what Full screen mode does.
I do not see this problem on my Geforce GTX 550Ti machine. Performance is the same(50-75FPS) for both "Windowed" and "Fullscreen". More details in my bug report if needed along with machine specs.