Ended up going with the Alienware Aurora because time is money and I don't have enough time or patience to research/sort out individual parts to assemble.
I'm still fairly cheap, so I started with the lowest end config, then picked the highest end CPU option (OC'ed 8700k) and ditched the ridiculously overpowered graphics card in favor of reusing my existing (and good enough) GTX 750Ti. Bought my own M.2 SSD to save a little more.
Haven't had time to formally benchmark and try out the OC options, but some initial runs show that the system as configured runs on par with the top-end line on the latest MAME Benchmark sites (krick's OC'ed i7-6700K @ 4.5GHz).
Final cost is on par with my previous (7 year old) desktop system (~$1400 before the SSD upgrade). I plan to update with some bench numbers later once my schedule allows.
Edited by AaronGiles (11/09/17 12:30 AM)