I think you misunderstand most of what is happening. I will try to clarify:
Turning off render preview will not have much effect on the timing for well written graphics drivers. That's why it's on by default. However some drivers are VERY slow at copying raw pixel bits to the screen using OpenGL - particular some low end, integrated grahics drivers - so I added the ability to turn it off. You SHOULDN'T see much difference on NVidia cards :-)
If your computer DOES speed up a lot when you disable render preview, then you have a BAD driver.
The reason that Anim8or seems to lock up during a render (it doesn't really - it's just fully busy doing the render. It ignors all the thousands of Windows messages it gets per second because some drivers are TERRIBLE at this and slow down horribly even they aren't doing anything - thay just are inefficient - So I ignore almost all Windows messages when rendering. You should still be able to ESC out of the render. Anim8or is not frozen by any means -- it's just ignoring you

You should NOT see much of a speedup changing the priority. Anim8or will normaly get 99% of the CPU time. In fact I am thinking of lowering the priority so other Windows tasks won't get starved for CPU cysles. Windows isn't a very good OS at switching between tasks. MACs, for example, are much, much better at it.
Your graphics card is a very good one for Anim8or. I have an 8600 on one of my computers at work and it runs Anim8or quite nicely.
Hope this helps clarify a few things (to you and others).