FPS Drop

I were testing a snapshot (14w18a) and i created a custom world, a preset. ("Mountain Madness".) I thought, "Wow! Jeb and the others made a really good job on this SNAPSHOT!" And suddenly, i get a FPS drop. Never happen'd in any game before and not even minecraft. I've got a pretty sharp pc so i don't think it was it (specs below) so i thought that i could report this issue here

PS: Every world i tried (Mountain Madness, AMPLIFIED, Normal) FPS dropped me Hope you (or me) can solve this =)

Specs:
Intel core I7 4770k 4.2Ghz (CPU)
MSI GTX 770 (GPU)
Corsair Vengeance Pro Series 8GB 2133Mhz (RAM)
Corsair 850 RM Gold Modular +80 (PSU)