meowmix44 :
I replaced my ASUS DC2 7970's old sloppy thermal compound with a small bit of MX-4, overclocking was easier since then and I now stay in high 60s/low 70C under load and with an overclock. I'd recommend MX-4 because it doesn't conduct electricity and does not take any time to bond. (Silver 5 will bond over a longer period of time) I use MX-4 on both my CPU and one of my graphics cards. Make sure you eliminate all of your old compound before applying the new.
Note, your card seems to not have any problems, although it could possibly improve. I am sure that if you replace the old compound with new higher quality thermal compound, you should get better temps. When I removed my card, I saw that it had a huge glob of thermal compound everywhere, just apply it in a small amount over the GPU die.
Artic Silver mx-4 is one of the best thermal pastes you can buy, where as you stated, stock and cheap thermal paste actually is a type of ceramic, it hardens over time and effectively begins to become an insulator. Mx-4 is great because it is a polysynthetic blend made up of Non-Capacitive, Non-Electricity-Conductive, Carbon-Micro particle Based Thermal Compound that is also Non-Curing, Non-Corrosive, Non-Bleeding, And has Low Thermal Resistance ,High Thermal Conductivity Dissipating Heat Efficiently. Making it hands down one of the best thermal pastes you can buy. On the other hand the absoulte best is the artic diamond compound.