Ken,
1800 oz-in steppers are HUGE. I can't imagine you'd need anything that size. And, such large steppers will be SLOW, due to high inductance, and high inertia. With servos, the continuous motor torque ratings will nearly always be considerably lower than comparable steppers, because servos are nearly always geared down 3 or 4 to 1. Servos essentially constant torque, and are typically capable of high RPM, while steppers always lose torque at higher speeds, often precipitously. So, steppers are usually used direct drive, while servos will usually be geared down. As an example, my 9x49 knee mill uses DC servos rates at 850 oz-in peak, 140 oz-in continuous, and can run up to 4200 RPM. With 2.5:1 belt reducers, driving a 5-pitch ballscrew, I get 350 IPM rapids, and enough thrust at cutting speeds to break a 1/2" endmill without losing position. A stepper conversion on the same machine would probably use steppers in the 900-1000 oz-in range. It would not get the same rapid speeds as the servos (probably top out at 120-150 IPM, being RPM-limited due to torque fall-off at high RPM), but would be reasonably comparable otherwise.
To properly design a CNC conversion, you have to know the required torque to move your machine, the inertia of the mass to be moved, and the target performance you wish to achieve. Armed with that information, you can design a drive system, servo or stepper, that WILL perform as wanted. Most people seem to just ask "What motors should I use", then buy something close based on the recommendation of someone who may have never even built a machine, pick some drivers and power supplies based on what they can get cheap, they they're surprised when it doesn't perform nearly to spec. There is no substitute for doing the math. Trying to "over-design", by picking over-sized motors is just as likely to fail, just for different reasons. The screws, reducers (if any), motors, drivers, and power supplies all have to be designed as a *system* to work properly. If any one is poorly matched, system performance will suffer, often badly.
As for heat and noise - heat is really a non-issue. Yes, stepper motors typically run hotter than comparable servos, but they are designed to handle the heat, so it's not a problem at all. Steppers are typically a bit noisier than servos, with a characteristic "whine" when running, and depending on the specific driver used, they may "hiss" slightly when stopped. This is purely an aesthetic issue, not a functional one.
On most jobs, very high rapid speeds should not make a huge difference in overall run time, unless you're using pretty bad CAM software. Rapids should be less than 10% of the total run time on most jobs.
Regards,
Ray L.