So I currently have both the X51 with upgraded 670 card (Looking to sell, please PM) and the Revolt with Titan card.
My experience with the X51 has been great. No issues, easy to upgrade. Loved it
Bought Ibuypower Revolt, currently having issues with sound distortion through HDMI of Titan GPU. Luckily, Ibuypower is located 10 minutes from me, so getting this issue fixed would be easier than if I lived miles away. So I will post another update once I get receive my fixed system.
The only thing I would currently say about Ibuypower, is to prepare for a long wait. By visiting their forums it looks like they are extremely backed up. It took me almost a month to get my system and it takes a while to receive any electronic email update, so you are somewhat forced to do a live chat or call for an update.