If you want SLI, do as per
http://forum.1cpublishing.eu/showthread.php?t=23199
Your 295GTX is not a very good card for DX10 so this is your bottleneck. It also has 900Mb VRAM per GPU and this is also a limitation for this game (CoD needs >2Gb VRAM to run well).
You did not mention whether you are running WinXP or Win7-64bit, from the amount of RAM you have I presume you have the second (Win7-64bit). That is good because otherwise your operating system would also be the bottleneck.
~S~