First off, the Hankook RS-2's can't hold a candle to the Dunlops. The Falken Azenis are even still better than the RS-2's. The RS-3 is coming out, thats why the RS2's are on clearance; well, that and the fact that they were never really that good. They are a VERY grippy street tire, don't get me wrong, but at autocross, they give up a lot to the other tires mentioned here (particularly the Star Specs and XS). If you are a mildly serious autocrosser though, you'll want better.
If you are going to use them as street tires, I would get the Dunlops. The Yokos are awesome, but uber expensive by comparison (same with the 'Stones). The Khumo's are great tires with slightly better dry grip, but have more trouble in the cold and are terrible in the wet. For autocross ONLY ST competition, I'd get the Khumo's, but for a street tire/autocross tire, the dunlops are better IMO. They give up VERY little at autocross to the Khumo's, but are much more streetable (a couple tenths on a 60 second course at most). I'm pretty much in the same boat you are, in that I use my autocross tires as street tires. I've had two sets of the dunlops, and when it came time for me to buy tires again recently, I looked at the Khumo ('stones and Advans were out of my price range) I decided on the Dunlops again. They've been great. 16-17k miles and autocross duty (about 10 events per year and one school on average). They kick the ever living crap out of the Falken's I had before them (and are FAR more streetable). Here's a good review from tire rack.
If you do get the dunlops, 225 will probably be plenty for you. They run RIDICULOUSLY wide. I've got 225/45-17's on a 7" rim, running much wider on that rim would make me nervous (others may tell you different). I'm limited by the class rules in ST to 225 width, so its not even really an option for me anyways.
In short, Do it. Dunlops, 225/45, you'll LOVE them (and you'll want to ditch those RS-2's on the 30 and replace them with Dunlops). Theres a reason I'm on my 3rd set of them.