I was going to mention this in the thread about the "Millennial Troll PC" someone else was building, but then realized it was the wrong era. A BTX Netburst 1.4 GHz RDRAM build would be hilarious.

I've built a Frankenstein Dell computer which consists of an Optiplex 745 motherboard inside an Optiplex GX520 case if that counts. Then again, it's not necessarily a gaming rig, it's more of a video editing/transferring rig.

The major downside of BTX is that video cards that took up two expansion slots didn't fit in most of the cases. I've had to remove the VGA header from my nVidia Geforce GT 610 video card to make it fit without sacrificing a PCI slot in the Dell computer, since that card has DVI-I (which works with VGA adapters) and I really only use one monitor on that rig, it's not a problem.

I've always looked at BTX as another P4-inspired "Rambus moment" for Intel. It was only a thing because the Prescott P4 ran so dang hot, and the large central fan helped keep things cool in cramped OEM machines.

AMD completely ignored BTX; they claimed that Athlon 64 ran just fine on the ATX motherboard most people were already familiar with. And of course, Athlon 64 was the enthusiast's CPU of choice at the time. Even Intel gave up on BTX after launching the cool-running Core 2 processor, though Dell and Gateway continued using it for another year or so.