I actually have mixed feeling about 1.8 versus 1.7.10 -- on the one hand it actually does seem to improve performance and efficiency a lot over 1.7 (on that mater I like 1.6 or 1.8 over 1.7 -- to me all 1.7 versions seemed awfully laggy, especially during world-gen). OTOH, 1.8 seems to be yet another break-everything update (Forge hadn't even managed to get its block registry working last I checked), with another probable break-everything update looming to come out just as or before many of the big mods update. So, take your pick -- problems either way. I still develop for 1.7.10, then port to 1.8 for the "latest must be the best" crowd, with work-a-rounds for the places Forge is still broke (and wonder if back porting wouldn't be just as good or better).
For my current setup in 1.7.10, Fastcraft fixes literally all issues I have with World generation stutter/lag. But without that little gem, yes, I agree with you entirely that 1.7.10 has some of the worst World Generation lag I've had to deal with.