Good point, Jazz. I use steppers, with a BoB and a PCI parallel port adaptor card. My motherboard, bought about 18 months ago, is an MSI A55M-E33 with an AMD processor and 8G RAM. I see from the place I bought it that that MB is no longer available, which just about sums up the problem with PCs and, particularly, motherboards - I've never seen a list of "suitable" MBs that actually has anything on it that I can buy! I did the usual LCNC latency test, and have ended up with a kernel speed of 28KHz (from memory) but my router is not that fast and fastest rapid feed only needs about 8KHz, so there's plenty of headroom.

I wasn't aware that LCNC could support servo encoder feedback directly (but I haven't needed to, so I've never looked for this feature). That would certainly put up the required kernel speed; on the other hand, the OP was talking about a mill where speeds are much lower than a router, so maybe it would be OK. All the same, if you are going to the lengths of using servos and the complications of feeding back encoder output to the motion controller as opposed to a self-contained servo controller, then I'm sure that it would be worth going to the cost of an external motion control card that can guarantee performance.

Doing some simple back-of-envelope calculations for a sanity check - my current router uses a 1.5mm pitch leadscrew (best Screwfix stainless threaded rod and everything...) and 800microstep/rev. 900mm/min max feed (at which point the leadscrew is not quite whipping too much) needs a pulse rate of 8KHz. Go to a 5mm pitch ballscrew and that would give 3m/min rapids with same pulse rate; LCNC tells me that it could run at least twice the current pulse rate so that would give 6m/min rapids and still not be pushing the limits too much. So, with steppers a cheap modern MB running LCNC would comfortably handle a typical "hobby use" router. I'm going to a CSMIO-IP/M for the next machine, but more for peace of mind and general electrical/EMI proofing than real need. Servos - different story.