Disc Brake Conversions

Has anyone went with the larger rotors offered in the aftermarket now? How about converting from rear drum brakes to rear disc brakes?
Any good kits out there?

I put a set of SSBC on the rear adn it worked fine but I am not getting awesome pressure. It stops but feels like it's not grabbing as much. I called the company and they said to have GM reset the ABS but they have no idea what I'm talking about. Good kit if you go off road at all because they don't clog up anymore.