on my 600 the rear dunlop tire had over 20,000 miles (35-38psi). Something is definitely wrong on your wear mileage. There are better handling tires that I could have bought, but chose dunlops again for the rear for the mileage. Cycle Gear has
DUNLOP D404's (170/80-15 rear) for $135 (free shipping over $79). And unlike some suggestions of where to buy, I have personally bought various items from this online retailer and without problems.
RONW