Here's what Lollar say about the Strat Dirty Blonde pickups:
The Lollar Dirty Blonde strat set is a mixture of Lollar Vintage Blonde® strat pickups in the neck and the middle positions, and the Lollar Special S Series® strat pickup in the bridge position. This combination gives many players the “best of both worlds.” The Lollar Vintage Blonde® neck and middle offer a bit more sparkle, chime, and top end bloom. At the same time, the slightly higher output Lollar Special S Series® bridge is just a bit darker and rounder that our other strat style bridges. In most cases this helps lessen that typical strat “ice pick” bridge sound.
The Lollar Dirty Blonde strat set is interesting for yet another reason: Nash Guitars. Basically, if you wanted to order what you hear in a Nash strat, you would want to order a Lollar Dirty Blonde strat set.