The back plate is manly for looks and not so much fro cooling I have a back plate on both of my 460's and with or without the back plate the temps never change. They stay the same 45-50 deg.
Intel i7-2600K, Gskill 16GB (2 x 8GB) 1600Mhz, Samsung 830 500 GB SSD, WD 500 green HDD,EVGA GeForce GTX 460 SSC+ In SLI, Asus P8Z68-V PRO/3GEN, Cool Master Half X Case, ThermalTake Grand 1200, Win 7 x64