Futuremark Vantage
A popular measuring stick of performance, Vantage runs a number of synthetic tests to assign a value to both your CPU and GPU, as well as an overall score. We used 'Performance' mode for our tests.

With the three GTX 280 cards, our system doesn't have much of a chance to catch up. However, you don't play synthetic benchmarks, you play games, so let's see how the Neptune fairs in the following tests.
Unreal Tournament 3
We used a 32 second FRAPS run on the VCTF-Suspense map to get a framerate average in UT 3. We ran the game at a 1920x1440 resolution.

From previous testing, Unreal Tournament 3 seems to be very reliant on the speed of your memory to feed the GPU. For this game, There did not seem to be much advantage going with three GTX 280 cards (over one), because once you get over 200 FPS, any further gains are almost impossible to notice when playing the game.
World In Conflict
This popular W.WIII RTS can be fairly strenuous for a system to run. We used a 32 second FRAPS run on the first level of the demo version of the game; starting from a saved-game position we ran from one end of the map to another. We used 1600x1200 with graphics set to 'Very High' quality.

Our overclocked benchmarking rig seems able to keep up fairly well with the Neptune here - but the Neptune still takes the cake.
Crysis
What benchmarks would not be complete without Crysis? To bench this game, we did a 34 second FRAPS run on the 'Awakening' level, at a 1920x1200 resolution using 2xAA.

Multi-GPU scaling must be much better implemented here in Crysis -- the game ran very smoothly on the Neptune.