I decided on the 12" from what I read about converters on gnttype.org. I'm not looking to build a monster, just a mild nice street setup. Something that can be taken on a long trip or cruise the town. From everything I've read the biggest I would go is the 3200. But I don't know enough about the different size converters to pick the right one for either turbo: 9.5" 10" 12", multi-disk, single disk?
The turbo vendor should tell you the suggested stall for whichever turbo you buy. 12" converters should not exceed 2800 rpm as they become very inefficient as the speed increases. If more than 2800 rpm is required, I would suggest you go to a ten inch converter.