AnandTech has a head to head review of 2 tiny SLI systems.  The Monarch Hornet Pro SLI Revenge Micro-ATX and Shuttle’s SN26P SFF, both fully capable of running 2 high end cards in SLI, so they fit a lot of power into a very small space.
“The twist comes in the inclusion of a system that isn’t a Small Form Factor design in the strictest sense of the word. We have the latest Shuttle SN26P SLI-capable unit, and we also have Monarch Computers’ latest foray into the small computer world, the Hornet Pro SLI Revenge. Both are quite a bit smaller than your typical mid-tower ATX case, but where the Shuttle is targeted primarily at reaching the smallest size possible while still offering competitive performance, Monarch goes with a micro-ATX (uATX) form factor. In exchange for size, you get some other options, which we’ll discuss more during the course of this review.”

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