wat size is your HRE's? cuz with a 20 mm spppacer you'll need a fender roll. so a 15 mm should be fine and youre HREs will be more flush looking. now if youre HREs are like +40 then you cant really ue the 20mm spacer without furious fender mods. and theny yu just wasted 100 bucks.
but then again if youre buying HREs 100 probably doesnt matter
I would make sure the stock studs are long enough with the spacers for the wheels to be safely mounted. Reducing the threading by 15-20mm is quite a bit, you will probably need longer studs if you don't want a wheel coming off at highway speeds.