I've got a map, created in 1.7 and I've got approximately 30-40 FPS (My computer is correct). But when I join this map in 1.8, on some chunks, I've got big freeze (in 1.8 I've 40-50 FPS) and my FPS fall to 7 and come back to 40 immediately.
It's not a corrupted map (http://uplmg.com/mul)... and I think, it's not my computer, because other people try this map on my server.

If you want more information, tell me.

Edit : I'm french so, if you don't understand my english, I can explain more !

Mr_coco29