Great! I am trying to hit my design specs without slipping into my usual (expensive) over-engineer everything out of fear...so a 10A power supply is even better.
(ViperTX...do an ebay search on CMC servos, that's how I found these piecemeal, over a two month period of looking...Al says they are also EG&G, a good piece of info to have when searching).
Thinking about this some more...if I convert to SI, the 456 pounds of thrust is 2,028N.
If the gantry weighs 200 pounds, that's 75Kg, or 735N of downward force due to gravity.
If using linear slides, the coefficient of friction is a ridiculously low number (something like .004), so the force of friction is pretty much negligible...maybe 3N...so net motor (applied) force on the gantry is 2,025N.
If I calculate acceleration, Force = Mass * Acceleration, or A=F/M, and A = 2025/75, or 27 meters/second/second
If my desired jog speed is 175ipm (or 0.074 meters/second), it should take about 3 milliseconds for the gantry to accelerate to the jog speed. Turnaround time should also be similarly "instantaneous".
Boy, I hope I've done this correctly. 
It would seem that the only 'real' forces I have to worry about are:
1. Friction of the cutting bit through the material being cut, at the desired cutting speed.
2. Overcoming gravity for the z-axis.
Intuitively, it would seem that I've got plenty of power at the router for woodworking or light aluminum. Provided I'm not doing something stupid like a 2" deep cut in maple, using a 3" molding bit.
What was worrying me was some of the reading here I've done about people buying much larger servos. I think I saw specs like 200 oz or more. Maybe they were talking about peak torque?
My little motors are 64 oz / 256 oz after gearing...so either I missed something, or we are talking about continuous versus peak torque, or everyone else is over-spec'ing their motors.