1. Monitor temps with Rivatuner and Atitool in Artifact Tester at each frequency.
2. Provide air-flow on the card's memories. I do it by using a 70 mm fan over a ~55-60 mm GPU radiator (from an Arctic Silencer), thus providing good air on the memory chips.
3. DO NOT volt-mod the memory with the above resistor 437 .. I think it does exactly the opposite: it decreases memory OC. Wipe any pencil trails from it with acetone or technic alcohol.
Leave only the GPU mod. If the GPU OC starts to decrease, it's time to wipe-out the pencil and start over with it.

Good luck!