When setting up the motor velocity and accel you should be able to test from within the motor tuning page as you tune by pressing up and down arrows on your keyboard.
Forget the slow jog, you need to find the sweet spot for your rapid as if you rely on a slow jog % your motors will stall as soon as you either command a G1 move faster or command a rapid move (G0)

You could try setting Sherline mode as enabled and restarting Mach to see if its any better, the other thing is run drivertest.exe (with Mach closed down) and see what it looks like.

What voltage are you using for your power supply to the drives?
Hood

Unless I missed it in my quick read, the motor voltage has not been stated. A common problem with newbees and steppers is to supply the voltage that the motor spec states. Steppers should run on 3 to 6 times their 'rated' voltage. I have not messed with steppers in a long time and I don't recall exactly the technical reasons why the stepper rating is so far below the correct operating voltage, the rating is voltage per phase or per winding or something like that. In any case, a stepper will be very lethargic running at its 'rated' voltage and the proof here is the inability for the stepper to accelerate to keep up with the step stream. Steppers are very slow in any case and certainly should be able to reach the few hundred RPM they are capable of. If your voltage is correct, I would suggest you remove the motor from the machine and try to spin it up on the bench. Even an 'un manly' stepper can reach full speed with zero load    . 

Steppers draw full power whether they are moving or not, that is why they hold so well, and as a consequence they are designed (insulation and lubrication temp specs primarily) to run hot . . . that's hot, not warm. Perfectly normal, even if they are not moving. Imagine a skinny old guy with his neck stretched out as far as it will go, holding his breath with his face beet red and his eyes bugging out . . .  that's how steppers are all of the time . . 

However, they will only get to a certain temp and then just stay there. On the other hand, a normal DC motor under a heavy load (holding up an uncounterweighted Z axis, or otherwise held off of its commanded position for example) will continue to heat more and more until it self destructs, so you do have to pay attention to temp on those motors. 

 

I found from testing here that some steppers will start to act funny at higher temps no matter what the rating is, missing steps, etc, etc. The higher voltage will allow higher rpm as the pulsing goes from a rather dc to a ac and that frequency gets limited similar to an RC circuit. In fact, one can actually mount the motor and turn the shaft at different rpm and measure the voltage generated from it and see at what rpm it drops off. Any voltage in excess of that is useless and the drives may not be able to handle it.

Irrelevant of the above, I would imagine that  the torque is at the bottom of the motor curve when at 200 in/ min. The motors are underrated for even a small metal lathe in my opinion even with the gearing.

Fwiw.....
RICH