Well I  decided to try the ibl on a scene that without the ibl takes about 40 minutes (fairly complicated with a lot of larger models in it etc.) on an i7 with asus ultimate board and 6 gigs of ram. The estimated time in AA is 2 days, 5 hours ,58 minutes. Thats a real lot of time difference.  Plus when I tried to stop the render it just froze Bryce abd that was that. Will try different settings and see what happens.