I suggest any one who wants to overclock reads up on it 1st.
Go here to see a list of results for various opteron overclocks
Opteron 939 overclocking
The 1st post has the results grouped together with all relevant material, some impressive results.
Hypertransprt multiplier can be lowered to prevent instability my opteron is running on x3 instead of x4. From what I know there is no adverse effects on performance untill hypertarnsprt goes below 600mhz.
Always use an aftermarket cooler if going for the real oc push, stock is good for modest overclocks
Ram temps will not increase unless you push the voltage to them
Unless you buy performance ram say DDR500 then for high overclocks you will need to run a ram divider, my overclock does as my ram will only hit 230mhz. A ram divider will reduce the fsb to levels that your ram can handle so therefore allowing the processor to run faster and your fsb to run normaly.