That kind of negative rear camber is typical for track use but not street use. Depending on what brand and type of tire you will probably see excessive wear around 8-15k miles. Keep in mind also the tire manufactures don't have any regulations for their sizing. So for example a 315/30 for one...
The performance advantages of the DH really show up when you take it to the track. IMHO if you don't plan on ever going to a local HPDE then save your money and go with a GT PP.