I recommend you go for the biggest unit size (80/120/200). I had always played MTW on this from the start, but have now spent a year playing with the next size down (66/100/166). I really prefer the largest size, for numerous reasons, and am planning to revert to that in my next campaign (once I've finished modding). Most units will take 2 years to complete on this setting, and some will take 4. I think the Royal Knights and Ghulam Bodyguards still only take 1 year due to their small size.