So, has anyone done this before?
I have fans on my heatsinks, but they're not spinning right now and they generally won't in the course of an average day. My system temps are 30C on each CPU and 33 on the motherboard. Under load they go up about 3-5 degrees. However, the system is located in my laundry room which is only about 10-15 C (I pass all my cables through the wall). So if you add 5-10 degrees to those temperatures to arrive at a more normal room temperature, you're looking at load temps of about 45 degrees - which isn't that bad at all. Certainly within Intel's specs and should not pose a problem as you aren't overclocking.
Try also using a duct from one of your intake case fans to the heatsinks. That will help.
There is a warning in the bios for overheating. Should I use that and what max temp should I set it to?
50 degrees is probably good. It's a little too high for comfort, but running at that temperature won't damage anything.
What is a good freeware, cpu temp monitor utility?
Motherboard Monitor is good but it's no longer maintained. The last release will work fine though. There's also Speedfan, which will also automatically control your fan speeds using PWM. On Linux, *BSD or other *NIX, use lm-sensors and Gkrellm for a front-end. On BeOS, use BP6Mon (available from BeBits).
How low could I expect to go on lowering the cpu voltage?
See my signature. If I didn't overclock I could probably go lower.
Maybe I should try a one of those cpu burn-in programs for testing. Any recommendations for a freeware one?
There's a bunch you can download
here. You can also use seti@home. However, because you're running an SMP system either get a program that is multithreaded or run two instances of a single-threaded program.
I realized at least I need to keep the heatsinks on the 500's.
Ummm... yeah. Don't take those off.