dtango,
I primarily fly the P-47. It has some good zoom climb capabilities but those need to be addressed with some caution. I.E. how close your opponent is and what kind of plane it is. The Zoom climb of course works best after a fast dive.
-Speed
I dive on an opponent as fast as I can get. It depends a lot on the amount of room you have to dive in as to the speed you attain, but I am generaly going over 450 mph when I reach him. The P-47 has good control at high speeds and that is a good tool when trying to loose someone also, many compress long before the 47 does.
-Steepness of climb
If I am diving on a bomber I make a steeper climb than if I am diving on something like a N1K, those guys can follow you fairly easily in your climb if it is too steep. I often will extend and make a very shallow, low g climb once he is behind me over D1.
-Unloading during a climb
As soon as possible I try to reduce the loading to the normal 1g, this of course helps retain your E.
-G-loading during beginning of the climb
This is target dependent. As I stated before it depends on the opponent's ability to zoom up after you. Of course if you find yourself close to the ground it would be wise not to run into it so use what is necessary
.
Hope this answers your questions.