Just use the most up to date. Check out this thread, use the modded BIOS. I am using modded 1306 but also had good luck with the 803 (iirc the e8400 @ 4.0GHz was using the 803). All versions of the BIOS have a setting that removes vDroop, you can choose to use it or not.
Both are great boards, if I had to buy one right now I'd go with the P5Q Pro just because it's cheaper. I've actually owned three P5Q Pros, one with a Q6600 @ 3.6GHz, one with an E8400 @ 4.0GHz and then the one I'm currently running with a Q6600 @ 3.6GHz.
The memory is running at 900mhz, the FSB X 2 = memory speed if running @ 1:1.
Back on topic, this is a great kit of ram, very overclockable. I kust bought another set a few days ago but all of mine do DDR2 1000MHz very easily.
There is a memory remap feature, or something like that, that you have to enable. You can try using a lower multi and try hitting 3.6 (8 x 450 instead of 9 x 400) that way but you seemed to be going fine using the 9X multi so I would just stick with that.
That's why it's single channel, because one is in the black slot and one in the yellow. If you put both in the yellow or both in the black then it will show up as dual channel. I have a P5Q Pro and it's the same layout.
Make sure you have the memory plugged into the right slots. Either both in yellow or both in black.
I know that kit of memory, that is an awesome kit. I've had three kits and they all easily did 1000MHz+ @ 2.1v 5-5-5-15. Unless you are very unlucky or they changed the chips they were using in...
55-58c seems right for where you are now. Your ram shouldn't be running any faster than PC6400 as long as you set the FSB : DRAM ratio right (should be 1:1, then @ 400 FSB your ram is running at PC6400, if FSB : DRAM ratio is 1:1 then basically your ram runs at what ever your FSB is, muliplied...