You can cancel a render in P6. You can do a small part (test area) of a render in P6. You have material groups to save in the matroom now. One click in P6 now loads what took a lot of time in P5.

P6 tells you that it cannot complete a render where P5 just froze requiring data loss on a reboot...Ctrl/Alt/Del...not good for your pc

P6 has AO. IBL. Advanced RayTrace with blur..

Keep your drives defragged and updated. Case clean. Fans cool and you'll be fine. And stay under 1.8gigs of Real memory in your scene.