questions for air combat planet geeks

[vicviper]

Hi, I'm working in a sort of flight simulator a la "ace combat", but I'm having some troubles making the planes easy to pilot and still look minimally realistic.

Since I've noticed here there's a lot of people that has lots of knowledge about real airplanes, I thought this would be a good place to ask...

talking about modern fighters (none in particular, all averages)

which is the usual speed at which fighters usually fly, in a CLOSE dogfight?

when over Mach 1, it is easy for a fighter to change direction easily? or it must do it very very slowly, almost in a stright line?

when a fighter is flying in a straight line, lets say at 800km/h , and suddenly does a hard change of direction, like 90 degrees, how much percentage of speed loses?

below mach 1, fighters can change direction at the same pace, regardless the speed they fly?, or the faster it flies, it is harder to change direction?.

that's all, hope someone can answer this