I bought a used XPS 8500 motherboard on eBay, installed it in an aftermarket case with 3570K CPU and 8gb of G.SKILL DDR3 1600 and it's been rock stable and very fast. However, the OS is Windows 7 Professional and the BIOS is set to Legacy Boot.
Is Windows 7 an option? The XPS 8500 seems to have issues with UEFI, Secure Boot and Windows 8.