I got the XR-E R2 for it, slightly better than the Q5. According to Match's tests here, the XR-E R2 max's out at 2.1A. You could get this driver: 20mm driver from I-O, and double up the 7135's, or try to go at higher amps with a 20+17mm board/driver sandwhich but it may not payoff. I-O also has a 1 mode driver I-O 17mm 1 mode 2.8A, but that would require the 20mm adapter board.
Right now, I didn't put in the R2 yet and am wondering what to do about the driver.