Suzuki SV 650. Great bikes, lots of them around, fantastic aftermarket support. Lots of them are used as track bikes, so look for telltale signs of hard use. Check the engine cases, footpegs, and bar-ends for scratches. Look for indications that the oil drain plug may have been safety-wired. Ask for complete maintenance records.
Just because you have dirt experience doesn't mean that you need a GSX-R. Dirt riding is great practice for street riding, but you don't learn all the skills you need on the street from riding in the dirt. You'll rarely see other dirt riders doing their makeup while they ride, or texting. In transitioning to the street, you are going to need to learn how to deal with traffic. Stay away from the R1s and ZX-10s until you've gotten some time on the street.