I checked my active processes. Bingo! Sins was using well over a gig of RAM, more than half of my CPU cycles, and I'd somehow accumulated a 1.5GB pagefile beyond my 2GB of memory.For the devs, I still have that autosave if it'd be useful.
It sounds like you have a dual core CPU like me in which case Sins is actually using 100% of one of the cores, which is the reason for the massive slowdown.
Sounds like a problem that the 8600 serries has period. I get this massive slow down issue when I play games like Crysis and FEAR as well, if I exit and reload the game, I get another few minutes of play before the slow down occures.This is actually making me go out and buy an ATI card. Nvidia has been promising to fix this issue for over a year now.
I'm sorry, but have you actually read any of the posts in this thread? The person you have quoted stated as I have many times that this is not a graphics issue, as it happens when you aren't even watching the battle and the fact that Sins is using 100% of the CPU.