I would never consider a multi-GPU setup. I know from first hand that support on those setups ranges from pretty good to non-existent, but it is an area that receives only little attention once the initial multi-GPU launch is done (if there even is multi-GPU support). So future patches etc may introduce instability for those setups (and they are often unstable at launch with quite a few issues) and only luck or a driver update (1-2 months) will fix it.

Additionally, with ever increasing resolutions and complex rendering pipelines that need an increasing number of syncs between the individual GPUs; SLI and CrossFire bridges are becoming more and more of a bottleneck.

Would not recommend.