I found a way to test bandwidth
and popped my GTX 660 into my HTPC which has a PCI-E v2.0 x16 port. The results were as followed:
- Main PC (PCI-E 1.1 x16) Average bidirectional bandwidth in MB/s: 1928
- HTPC (PCI-E 2.0 x16) Average bidirectional bandwidth in MB/s: 5868
So that answered my question, the GTX 660 was able to utilize 3 times as much bandwidth in a PCI-E v2.0 x16 port. I'm not sure if that's saturation of PCI-E 2.0 bandwidth also(overhead is excluded), but it must be close.
Alongside that test I ran the 720p FurMark benchmark and, to my amazement, the scores were exactly the same (<0.1% difference). My guess is that that's not a very good benchmark for evaluating PCI-E bandwidth performance which makes sense as it's goal is to stress the video card alone with the CPU out of the equation. Unfortunately my HTPC has too dissimilar a CPU (A4-3300 2.5GHz vs Q6600 3.5GHz) to do a fair comparison using another test.
I did however swap my GTX 660 into the secondary PCI-E v1.1 slot in my main PC and ran both Bandwidth Test and an ARMA 2: OA benchmark. GPU-Z reported that slot to be running at x16 but that cannot be correct (as the results will demonstrate) - the manufacturer's page states that it can run at x4 (AMD Crossfire only) or x1. The results:
- PCI-E 1.1 x16 Average bidirectional bandwidth in MB/s: 1928, ARMA 2: OA Benchmark: 56 FPS
- PCI-E 1.1 x1 Average bidirectional bandwidth in MB/s: 180, ARMA 2: OA Benchmark: 30 FPS
Given the enormous disparity in bandwidth available I'm surprised that the difference in frame rate isn't far larger than 50%. ARMA 2 is considered to be fairly CPU limited however so perhaps that test doesn't stress PCI-E bandwidth well either. Interesting results, but I still don't know if PCI-E v1.1 is a significant limiter for a single mid-range card setup. The results tend to suggest not, but are also far from definitive.
That said, my frame rates and frame times would improve significantly
from a faster more modern CPU regardless of PCI-E bandwidth. Perhaps it's time I put the old girl into retirement and dropped some dough on the 4670K I've been salivating over.