Even an R6 is a mental bike, I think you should be looking for something a bit less crazy. A CBF600 would be a good 500CC+ size bike which isnt too crazy. Trust me when I tell you the throttle on the R6 is more like an on/off switch. One twitch and the bike will be launching up the road faster than you've ever been before, if you meant it or not
My first bike was (still is) the kwak eqivalent and you just have to have absolute respect for it.
My top tip for you Jay is buy a brand new one that needs run in..... That way you'll get used to riding it slowly before opening the throttle and wheelieing up the road.
Even a 600 supersport is brutal. Absolutely insane.