I would very much like to have optifine, as fastcraft gives me a good FPS, but it's not all that stable. Optifine stabilizes it so it's not spiking all over the place. But there is problem, I can't run optifine without crashing, minecraft freezing up, or blocks missing. Also, it seems some people are using optifine with no problems but other's can't, which is weird.
So to the people who are running it, what version are you running? Blocks are missing when I use HD_U_A4, I crash when using smooth chunk loading on HD_U_B4, and minecraft freezes up using the the same version with multi-core chunk loading. Is there a certain version we have to use with this modpack or something?