Going from one card to two will probably net you an 80 percent increase in performance. You'll get less going from two to three, and the payouts dwindle even further going from three to four GPUs.
You can see scaling issues in Middle-earth: Shadow of Mordor. In this comparison chart, I've lined up the 4-way Epic Force X99 against the Mach V with its three Titan X cards and also threw in the result from our GPU test bed, a Core i7-5960X with a single Titan X installed. Running Middle-earth: Shadow of Mordor at 4K resolution with the HD texture pack installed you get a little more than a 20-percent performance increase going from three cards to four. That's really not bad. But then, a single Titan X gives you 35.6 fps; if it scaled perfectly, three cards would have been about 106 fps and four really would have been 142 fps. Multi-GPU scaling will vary from game to game and depend on the resolution you're playing, but generally it decreases as you climb above two cards.
That's the way multi-GPU setups have worked since the beginning. We've never gotten 100 percent scaling. Four GeForce GTX 980 cards, for example, probably would perform at or below three Titan X cards.
When you move beyond gaming performance, the Maingear hangs right there with the other Core i7-5960X-based 8-core systems. For example, in our Handbrake test, where we take a 30GB MKV high bit rate and convert it to a tablet-friendly format, the Epic Force X99 is just about dead-even with the Mach V system. Both run the same Intel CPU at the same overclocked speed of 4.5GHz. That's a testament to what Falcon is able to do with what is essentially an off-the-shelf, closed-loop cooler compared to the complicated custom liquid cooling in the Epic Force X99 box.
The Epic Force X99 definitely looks cooler, if that matters to you and frankly, it usually does to most people shopping at this end of the spectrum. The liquid-cooling on the Epic Force X99 also keeps it quieter than the Mach V. The Mach V is surprisingly quiet for a three-GPU system but it can't compete with a full liquid cooling setup, so that's definitely a win for Maingear.
Whiners, we're just whiners
We can't let this review go without criticism. However, the two things I want to complain about may not be within the control of Maingear. The first is storage. The Epic Force X99 came with three 256GB Samsung 850 Pro drives in RAID 0 and a 3TB Seagate hard drive. That's about a 1GBps of read speed from the RAID array which would be impressive if this were 2013. In the age of 2.7GBps read speeds from a single Intel 750 drive, it's a bit of a yawner. The issue, of course, is how to get an Intel 750 drive to even work in a system this heavily packed with hardware. You can read more about this problem here.
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