Stall speed varies according to the square of Gs. In a seriously interesting vertical maneuver, you could be cutting down the Gs to a fraction of 1 -- so the plane is still flying, just not fast enough for your control surfaces to do much good. Then the plane stalls, but again, given the speed, the effect won't be dramatic. You just slowly go ballistic. A big, heavy engine up front doesn't mean the plane is nose-heavy. In fact, conventional aircraft design and loading has as a principle the keeping the aircraft's center of gravity relatively near the center of lift.
The biggest thing that engine will be doing is trying to spin the aircraft around it.
So, in short -- when you go vertical, at a certain point you end up flying slower than you can effectively maneuver. Then you go ballistic. So you spend a lot of time hanging. In certain circumstances, you can use the propwash to control the plane. But in general, when you're in combat at a certain point staying vertical isn't helping things any more.
(then again, it's really cool when you're canopy-to-canopy with your adversary, hanging in air).
Oh yeah, and there's plenty of data on how planes fly, but my understanding is that the physics get really interesting in situations like this, probably far more so than any realistic flight sim can handle.
