Speed doesn't only help survival, but also helps killing a direct way (enemy can't escape easily, has much less reaction time) and - often overlooked - allows YOU to reach the enemy before your teammates in slower planes can do.
That's one of the biggest downsides in flying slow planes like a Hurri I or I-16 - you get your 12 cleared by faster & heavier armed planes before you can close in for the kill.
Good point. From a "game" perspective, I didn't think about that to be honest....and I should have as it happens to me quite a bit when flying the 110.

Experience has taught me to get fairly close before shooting. Why? Because the 12 clearing types usually don't mind flying THROUGH your stream of 20mm and 30mm i.e. Killshoot and *poof*...Instant Tower for you. So the choices are:
1.) Get close, make it harder for the guy to nudge in but run the risk of losing the kill to a faster plane
2.) Firing farther away but risk ending up in the tower due as a 51 dweeb comes blazing in to get the kill and runs through your fire.
Third option, of course, is to fly away from friendlies as much as possible...which I generally try to do...but it seems to be more and more difficult to as the decline in numbers tends to compress fights in the MA to a few very large furballs. Ah well...