can you post a screenshot of your scene, and details of your vray set up. sometimes theres not much you can do about rendertimes except for get more machines and split the render over several computers. 1-9hours is pretty normal, i'm waiting for a night time exterior shot to render at the moment at 3000px and its taken about 11 hours so far, and has about 8-12 hours left, thats due to the size and about 20 lights. you can try mess with the raycaster parameters to speed up your renders or other settings but it depends on your scene.
if its a single thread process theres not any you can do to force it to be a multi threaded process unless you are a genius and know how to hack software etc, hopefully vray 1.5 sp3 will have a whole load of improvments and optimizations.
don't know about this Nvidia afterburner thing, think you getting it confused with something else, if it was out there i would be using it lol