Same pc specs different fps

Me and my friend have built the same exact pc's except I have 16 gb of ram and he only has 8. We have both overclocked our i5 3570k's to 4.2 ghz and no gpu overclock on our gtx 660's. When we both play medal of honor warfighter and stand in the exact same spot facing the same way he has 80-120 fps and I only have 50-70. we both have the exact same graphics settings(ultra settings) and I don't understand how he has so much more than me. We have both checked our bios settings and we have both done the same things, oc to 4.2 ghz and turn off intel speedstep technology. I could use help from anyone, thanks.

Pc specs:
cpu- intel i5 3570k (oc'd to 4.2 ghz
gpu- nvidia gtx 660
motherboard- asrock z77 extreme4
ram- corsair vengeance 16gb ram
ssd- crucial m4 128gb
hdd- wd caviar black 1tb

these are me and my friends pc specs (except i have 16 gb ram and he has 8 gb)