makeparts, having done both an X2 with a G540 and just wrapping up a G0704 with a BOB, individual drivers, a motor control card, etc I can say that a system built up with a G540 is SOOOO much simpler! Very minimal wiring, nice clean control box, and no headaches. On my G0704, just laying out where to put 4 drivers (and I'll need to add a 5th for my ATC) in the box with a BOB and motor speed control, separate 5 volt power supply for the BOB was a challenge!
I cut a lot of Delrin, aluminum and brass with small (1/16 to 1/8" and smaller) bits on my X2 and made l000s of parts for my fishing reel kit business. It has been rock solid, reliable and no fuss.
I think folks go bigger thinking they may reuse motors on another mill someday, got a good deal on ebay, or whatever. I personally don't think bigger is better. I have had no problems milling steel with my X2 when needed. The biggest factor there was rigidity - do a Z column brace of some sort (you can read about mine and others here). I did the milling required for my G0704 conversion on my X2.
If there were a big brother for the G540 for these bigger mills I would have not blinked an eye to use it!
cheers,
Michael
Reelsmith, Angling Historian, and Author of "The Reelsmith's Primer"
www.EclecticAngler.com | www.ReelLinesPress.com