There is an Intel issue at 5:4 with high performance ram at tight timings. I can just feel the board wake up at 1:1 with PC4000 ram. The P4C800-E and 4PCA3+ can prevail through that and put up stellar benchmarks. I don't know what they are doing right.
I just tested a DFI 875P Infinity board last night. First tried XMS3500. I could actually run 280, 5:4, DDR440, 2-3-2-5 Memtest clean at 2.7 volt limit of the board!!! But 3DMark persistently locked up. I couldn't figure it out. If I dropped down to 270 it would pass, but Memtest was clean and the CPU was good to 279-287. I just could not get 3D stable. I was about to give up, put the board back in the box and sell it tommorrow.
Then I decided to try ADATA PC4000. Result? 283 fsb at 1.49 VCORE 3D stable. Stuck in an MO step 2.40C, never characterized before. It errored out at 279, 1.58 VCORE on the 4PCA3+. It is currently running 285 at 1.54 volts! And I'm not through yet; I will test how much higher I can get tonight. I have to run 5:4 on the ram since the sticks won't do 283-285, 1:1 at the max 2.7 VDIMM of the board.
But this DFI board is the best overclocking board I have seen so far, and I almost sold it based on performance with BH-5. I see the same problem with the Abit, Gigabyte, AOpen, and MSI 875P boards (all of which I got rid of).
Fortunately I can toggle between PC4000/BH-5 to find which works best with a board. Both ram work well with the Asus and Epox boards, BTW.