I'm pretty sure most of the performance issues are in NL2. it uses 4 cores but never much more than 60%. It isn't SLI compatible, but even with the 1 video card I can get down to 10 FPS and it doesn't break a sweat. it doesn't seem to utilize all of the resources available. I did recently get a SSD and I can tell you that helped with loading times A LOT. idk why but this is the only program I have any performance issues with, I can run Skyrim on ultra settings with all HD texture packs and still stays at 40 FPS. The graphics cards will help for sure but don't expect it to be %100.
stats -
AMD FX-8350 Eight-core 4.6GHz w/turbo
2x 4GB DDR3 RAM
Ge-force GTX 550ti 2GB vram
Ge-force GTX 550ti 2GB vram
windows 7 (64bit)
512GB SSD (main)
64GB SSD (page)
512GB HD (backup)
I plan to replace the 2 video cards by this time next year with 1 or 2 titans
.