I don't think they will sag that much, and if they ever did I would be positive it would be many miles down the road. Especially if your going to crank them up I doubt they would sag, ride quality may deminish a bit after cranking them. I'm not sure though as I have no experience with pro comp coilovers, just cranked coilovers. You might contact sonny at down south motorsports to see what they can do for you. I'm running 18" springs which means I dont have to crank them and you get an extra 2-2.5" of lift. You might also get in contact with sbchris, a member on here, he has had two sets of custom coilovers made.
The only reason I suggest this "custom" approach is because of the bumper, and the fact that the platinum rides like a caddy and I would hate for a cranked coil to ruin that for you. King, Fox, and sway-a-way (in chris' case) can all make you a coilover to suit your needs.
