- How well is AGA supported right now, for WHDLoad games and demos?
Almost everything works. Most "errors" which happen in WinUAE have been proven to happen on real hardware, too. If you find something which works differently from real hardware, go to eab.abime.net and report it as a bug.
- RTG gfx for desktop are supported right? On most any PC vidcard?
As long as there are proper Windows drivers for the gfx card, WinUAE can work with it, too.
- Is WinUAE on a fast PC "tight" such that things are synched properly, seem authentic?
You can configure it to run in A500 speed, in A1200 speed or as fast as possible. Chipset timing is correct in all three speeds.
- What is the best mode to run for a "super Amiga" emu station under WinUAE? Emulated 040? 060?
All CPUs are equally fast under "fastest possible" emulation. For highest compatibility you should use a 68020 with FPU.