As we've discussed before, motor current, generally discussed in amps, and torque, generally discussed in kg.cm, are fairly linear at the same voltage on similar motors. There are lots of ways to have motors that make less torque than they "should" but for this discussion we'll focus on good motors that make as much torque as possible for a given size / current / voltage / robustness.
Stall current changes roughly linear with voltage. So 1 amp on 2S will be roughly 1.5amp on 3S. Similarly 2.2amps on 2S will be roughly 3.3amps on 3S.
Stall current is just that, the maximum current it will draw if forcibly stalled.
Being able to stall them will depend on several factors, primarily:
2. Tire diameter
3. Weight on the tire
Smaller diameter tires with less grip would require a lot of weight on them to stall them. Large tires with lots of grip will be stallable with less weight.
The Malenkis all have Over Current Protection (OCP), so when they hit their current limit they stop supplying the current for 1ms. You can actually hear when this this because it makes a 1khz sound as they keep retrying.
The MNI-HV is rated at 3.5a. They generally test at just over 4a. A stalled motor quite literally turns the windings into an electric heater. That 4a "heater circuit" generates significant heat in all of the components. They won't die instantly or anything, but they also are not designed to have 4a coursing through them for very long.
In summary, running 4 Turnabot N10 (1.05amp on 2S) or N20 (2.2amp on 2S) motors on a MNI-HV at 3S is certainly "doable" and depending on weight, grip, and tires diameter you might still be "safely" traction limited. You MIGHT also be able to stall then hard enough for long enough to hurt the motors.