You should have good luck, you have a good board and a nice CPU, but the RAM will likely hold you back the most, especially if it's cheap stuff like you said. You will be running it at it's stock speeds to achieve 1:1 at around 3.7, which means you will likely have stock timings. To go 1:1 at higher than 3.7 on the CPU, you would have to overclock that RAM, and cheap stuff doesn;t take kindly to overclocking, and of course, you will have to loosen the timings more to get faster RAM speeds.......
The 9xx series Pentium Ds overclock like mad, the 8xx seires are supposed to be very good (havent played with one myself) but not as good as a 9xx series. With your board and 820, and RAM, I would say 3.5 would be a good goal to try for, but you never know till you try.
Keeping your CPU under 55c is a good general guideline, but it is always best to check the exact thermal specs for your CPU.
Intel Processor Spec Sheet
I checked, and both revisions of your CPU, the A0 and B0 have the same thermal spec and voltage spec.
64.1c and 1.4v max.
So, you want to try to keep it at 55c or under, but it can go to a little over 60c before throttling occurs. With a BT, you shouldn't have much trouble with that.
I'd be very interested in how your OC works out as I have only played with the VM version of your board with an old 533 bus Prescott, I'd love to hear how far the P5LD2 will go with a higher end CPU.