Based on the cards alone... the V3100 is based on the 9600 or X600 I think, the FX1000 is based on the Geforce 5800 (a suck card but pretty darn good for CAD stuff).
In CAD viewport refreshes, I believe the FX1000 would probably give some serious hurt to the V3100, but I don't have any benchmarks to offer. But that's the way I'd go, disregarding the platform entirely.
Bringing the platforms into consideration really bungs things up, I don't know enough about Xeon performance to recommend anything. The clockspeeds look similar so I don't THINK there would be a massive difference in render times, but I'm not sure.
Personally, I'd probably take the Xeons & FX1000 just for the video card.
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