The ASUS MARS II is really a monster graphics card. It demonstrates the awesome power of two GeForce GTX 580 GPUs running at full clock speeds. Thanks to the massive design improvements the card delivers an almost 20% performance increase compared to NVIDIA's GeForce GTX 590 at 2560x1600. This performance increase is actually more than I expected when I first heard that ASUS is working on their own dual-GF100 design. I thought "maybe 5-10% faster" but ASUS has exceeded those expectations significantly.
Being the performance king does come at a cost though, not only financially. Since ASUS did not use any power limiting measures to keep the card in a power and thermal profile, the card ends up using over 500W during gaming. All this heat has to go somewhere, so the decision to use a triple slot cooler design is justified in my opinion. Even with that, the card ends up being noisier than GeForce GTX 590.
In my opinion the choice to use "only" 1.5 GB of memory per GPU is reasonable, since almost no gaming scenario requires more memory than that. Maybe at 3x 2560x1600, but certainly not below. That's why I actually prefer the MARS II with 3 GB memory total, instead of a card that's $200 more expensive with an extra 3 GB of useless video memory. On the other hand, when looking at the MARS II as an "all-out" card, the extra 3 GB of memory would have been the way to go, even if it would not made any difference in performance for most users.
In terms of overclocking we see excellent OC potential for the two GPUs, not so much on memory. ASUS has put a solder pad area on the back of the PCB for extreme cooling users to disable overheat control, for example. Voltage increases are extremely limited though with only up to +0.025 V, so you will have to do a soldering voltmod for more voltage. Overall it seems the overclocking features are geared toward "normal" overclockers who increase clocks and fan speed and hardcore enthusiasts that are willing to take a soldering iron to their card. The overclocker group between that seems not so much the focus of this card, but given the pricing, this performance per Dollar aware crowd might not be so interested in the MARS II anyway.
Talking about pricing, according to ASUS the USD retail price of the MARS II will be a hefty $1499. Even when considering performance, features, cooler cost and limited edition I think that's simply too expensive. I could find a price of $1000 or $1100 reasonable, but not more. Still, kudos to ASUS for undertaking the MARS II project, which really shows what can be done today in graphics card design.