I guess you rig is not helping at all, as you might know Crysis 3 is the game with the best graphics so far... Do you play another video game like Battlefield 2/3?? any game where you can compare the FPS ??
NyxSlayer has a good idea, try playing a few other games and see if they slow down as well, install a game on 1 harddrive and another game on another harddrive, you will find out if its a harddrive issue or a different issue.
Another issue could be the temperature, I mean global warming does not only affects the enviroment, but our gaming desktops as well... xD try downloading a GPU monitor though
Ok i have installed the latest tomb raider and Dead space 3 and they both run on full graphics just no AA +- 60 - 70 fps my pc's temp is fine will test installing on diff hdd tonight.
I also saw last night sometimes i can play cry 3 on high with no prob with more demanding environments but then i get to a closed off location and it lagg so much i cant even play on low.
temperature may have somthing to do with it, hardware will slow down almost to a pause if it gets really hot, which will effect game performace, rivatuner or MSI after burner are 2 free overclocking tools that come with an accurate temp monitor.
The only other thing i can think of is that it may be windows 8.
I have checked my temp and everything is running at optimal temps.
Maybe your PC is on Power Saving mode.. ^^
I have checked my pc is not in power saver mode but thank you all for the trouble.
I have formatted my pc and installed windows 7 again and it seemed to have helped a bit.
turn off background services from task manager,,,, And the most important thing .... When playing games, disable your antivirus temporarily.... Install Service Pack 1 .... update your drivers and try also updating your Bios...