In the first example, you are being confused by NVIDIA's naming scheme. If you look under the card name you'll see that the higher framerate card has 512MB of VRAM. It is in fact a different GPU as well, G92 instead of G80. The SLI configuration is two 320MB GTSs which are older (based on G80) and had a few weird bugs.
In the second example, you're looking at a CPU bottleneck, and margin of variation between benchmark runs.
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