first of your temps are very low. high temps start at 60C and 70C is where you are really pushing your card. as far as thermal paste anything of quality will get the job done so other than that just choose a brand you like
. as far as overclocking goes manually set your dram timings to what the factory recommends, set your cpu voltage on manual, disable turbo and power saving in your bios, and finally start raising your cpu multiplier until your system cant run pcmark06 or prime95 without it crashing. when it does crash raise your voltage a couple of clicks (hit + while changing the settings) then try again at last known good multiplier. raise the multiplier again and test. when you reach a max clock ceiling or your V hits around 1.5 then lower your ram multiplier and raise your bus speed by 2-4 at a time and test. make sure your HT and RAM dont go too high you may have to lower their multipliers. also, if you get stuck at any point try raising your NB voltage a little bit.
keep an eye on your temps and ask any questions you need!