Minecraft does not render the world (blocks, the black lines around blocks I am looking at, and so on) at the full native resolution of my screen. It is instead rendering at the scaled, pixel-doubled resolution that non-Retina-aware apps are told about on a Retina OS X system.
I suspect that the problem is that LWJGL is not being started up in "High DPI Mode" as described in <http://wiki.lwjgl.org/wiki/Using_High_DPI_Mode>. By default, OpenGL contexts on OS X render in the scaled-resolution mode unless the appropriate OS calls are made to put them in native resolution mode.
I would like you to render Minecraft in High DPI mode, so that the full native panel resolution is used, and to do the appropriate scaling of mouse input positions as described in the article to make it work correctly.
This is probably related to MC-44739, and basically a confirmation of MC-32327 affecting the current version.
I have the same issue on nearly the same computer (one year older so 2.4GHz vs 2.6). I also posted a comment on MC-32327 with more information.