I need help!!

[x8bluestar]

Hello, my computer has a i7 950 oc-3.2+turbo on plus a xfx 5970 cooloer master 850 watts psu, 6gb ddr3 ram, motherboard Asus 3xtreme, i also play on a ssd drive.I play the game 1920 x 1080 full screen, No aa, drawing quality 8, Shadow highest, background drawing 5, texture quality/filtering max. Now my problem is once i put my drawing to 9 everytime i cast a spell my FPS drop 20-30 only while that spell is being cast, other than that my game runs at full 60 fps. now is there a way to help with this issue cause is kind of wierd, there isnt much graphical difference in the spell casting looks with drawing quality at 9, not enough to make this drastic drop of frames, just for that instant. can any1 give me an idea what could be happening i see peoples spec's and they have way lower spec's than my pc and they running the game at highest setting's.