So, heads up:
http://minecraft.curseforge.com/mc-mods/230020-cofhtweaks
It contains some miscellaneous tweaks and optimizations, including a back-port of the 1.8 render optimizations. Some testers have reported a 10x framerate increase (YMMV). So yeah, now there is literally 0 argument for going to 1.8.
No, it doesn't work with Fastcraft. They perform some similar optimizations and won't work together as a result. Or if they can, it's entirely on Fastcraft's end to integrate. The difference is that these are visible source and entirely above board, whereas the community at large still has no actual idea what Fastcraft is doing.
Even so, it is a BETA. Bear that in mind please.