One of the nice things of painting regular troops is that they all wear identical uniforms or at the very least, feature the same colour combinations. Even for Irregular mobs, the same colours will often reappear (skin, generic hairy warband brown etc...). This essentially means that in order to paint your army in the shortest timeframe possible, one has to adapt the Henry Ford method of painting. In other words you apply one colour to all your figures before switching to another colour. Some people actually paint this way and are able to process an insane amount of figs in one go, however, they are extremely rare and average Joe will certainly not paint all his 200 Romans in one batch.
The major downfall of the above method is that while it certainly will field your army in the shortest timeframe possible, you won�t get the satisfaction of a job well done until the entire army is actually finished. 200 figures with a flesh undercoat do not look as great as 3 fully finished figs and will certainly not give you the same level of satisfaction for a job well done. The amount of figures one can process without suffering painters drag is highly personal, in my case my maximum batch size is about 10 28mm figures, more than that and I don�t see enough progression to satisfy my fragile ego.
The amount of figures one can paint in one go is probably related to some aspect of personality. This brings us to the widely used MBTI personality tests, according to which one can roughly differentiate 4 fundamental parameters which make up the major aspects of your personality. One is Judging vs. Perceiving. A Judging person gets its satisfaction from achieving set goals and thus tends to be much more orderly, while a Perceiving person enjoys the process itself and thus tends to be much more flaky and in pursuit of a bundle of different things at the same time. This means that both types are probably doomed as the judging character is able to impose upon himself the ruthless discipline of painting 200 figs in one go but will not get any satisfaction till they are all done, while the Perceiving character can get enjoyment out of unfinished in progress figures but lacks the stamina to follow through and therefore runs the risk of never ever actually finishing anything before wondering off in pursuit of yet another new daft idea.
In the name of science and the possibility of achieving greater painting satisfaction and army production through adequate counselling and Zen meditation, let�s work out a J-P percentile inclination vs. batch size correlation plot here. I�m 11%P, batch size 10, what are you?