Its been a long time since I built my machine but with servos of ~50 oz-in continuous and 350 oz-in peak and 4:1 reduction the X and Y move plenty fast enough (100IPM) and the accelerations are enough to jump the machine around. I can go faster but at the time my old control system wouldn't let me with the way I had it configured.(problem with a high encoder count and reduction...). I can go faster now but still don't - you run out of space plenty fast on Y at 100IPM.
My machine BTW is a 12Z (the bigger RF-45 type) so my bet is that the smaller of the servos you showed would be fine.
Other consideration is operating voltage. From the looks of it the higher the voltage the higher the peak torque but the continuous torque remains constant, but the max speed drops too. If I were to do it again I'd go for a 48VDC system as my 75VDC is a bit scary with the amperage and voltage available - it can bite pretty hard. At 48VDC you're still up there in voltage but its a just bit safer - especially with cables running in and around coolant...
Mike