I've done the vmod to my 4870 I think its working but I have no idea where to measure the vcore either in windows or with a multimeter. I just soldered 3 10 ohm resistors together and wired it up to the card. Temps aren't bad on stock cooler around 61c load with fan at 52% and clocks seem pretty good with no artifacts but I haven't been able to increase clocks going from 40 to 30 ohms so I'm questioning the actual voltage. I think I'm going to try 20 ohms tonight for around 1.41? vcore.