Asus P5ND Motherboard
4GB RAM
SLI 8800GT 512MB
Plenty of memory (no solid state though)
Intel Core 2 Duo E8400 3.0GHz overclocked to 3.4GHz
I've been told the single best upgrade I could do was a more powerful video card. I've also been told my CPU really bottlenecking my setup (at least my SLI). Is this true? Would it bottleneck if I upgraded to something like a GTX 560 Ti?
To clarify, I was talking about the possibility of two new cards into SLI, not your current pair of 8800GTs.
Would it bottleneck if I upgraded to something like a GTX 560 Ti?
Yes, but the GPU is still the best upgrade for overall graphics performance. Let me explain, I'll substitute a E8600 for your CPU:
http://www.anandtech.com/bench/Product/54?vs=289
http://www.anandtech.com/bench/Product/54?vs=288
...scroll down on the links above for the benchmarks of Fallout 3 and Dragon Age: Origins. Fallout is completely tied to two cores, DA:O utilizes four cores very well and additionally, it isn't very hard on the GPU. Yes a very quad optimized game can show tremendous gains with a quad, but:
1: We don't know if Skyrim is well optimized for quads.
2: All the CPUs have decent frame rates.
3: There is still going to be some level of Gamebryo traits in the new engine. [Fallout 3's engine]
As for the GPU side of things:
I'm substituting your SLI 8800GT 512MB with a single GTS450 to compare to a GTX 560Ti. If you think I'm undercutting your GPUs, use a GTX 285 or GTX 460 768MB... but the performance is somewhere in the middle at best. Either way, the point is that with the GPU upgrade, the performance boost is across the board with all games. This makes the GPU the safe bet in regards to upgrading in almost all cases. A CPU has to be pretty crappy [or the GPU needs to be really good already] for CPU to be the primary concern.
http://www.anandtech.com/bench/Product/316?vs=330