I would say practice for accuracy because if your not hitting the targets, it really adds up on the time and I found that after doing a lot of practice on accuracy I could much more easily work up my speed.
Judge it by target, if you can hit a target moving go for it but if it is a longer shot or difficult then it makes sense to stop to make sure you hit it. But it all comes down to preference.
I think the best thing to do would be to do what I have learned to do with rifle firing awhile back, have someone else load your mags with some live and some dummy ammo, then try shooting and you will see if you are jerking on the dummies.
I've found what most of the other posts have, it really helps to stick just to one, the best shooters I know only use 1 gun and the smallest of changes can mess them up.
I have been using some 30 round mags I like a lot, with the anti-jamming insert (dont know technical name but it makes sure that the bullets dont go in and tip side to side) and have the spring that doesnt conform, when left with some rounds in them and was just looking for a 45 round mag that does the same and functions well, any suggestions?