Help to diagnose

Hello, I was wondering if any of you guys would help me to diagnose my problem.

I have an asus p4c800-e deluxe, a 2.4c, and 512 (2x256) OCZ pc3700 gold edition running in dual channel. I have been running for months on a mild overclock of 2.8.. making my memory run at 470 (235 fsb). It was all great.

Then, I decided to buy another gig of memory (2x512).. I looked into it, and my motherboard should be able to run two pairs of memory in dual channel.. as long as I have my 256's in either slots a1 and b1.. or a2 and b2. witht the 512's paired in the opposite. So I went ahead and bought a pair of OCZ pc4000 gold edition (not being able to find 3700, so I went with one step up, figuring it should be able to handle the underclock).

Now here's the problem. At a fsb of 200 (400mhz ddr), all 1.5 gigs will run in dual channel and be happy... but I want to run at 2.8 (235 fsb) like I have been for months. With just my old 512 it will work.. but it won't work with either all 1.5 gigs, or even just the 1 gig.

On the sticker, the memory says its pc4000, capable of 2-3-3-8 timings.. but even with worse timing, I cant seem to get it up to 470 mhz. So I would assume the memory I got just somehow slipped through QA and actually can't hold itself up... but just in case I thought I should ask around at a few forums. Also, if you guys know, what voltage is it supposed to require to hit 500 mhz?

thanks for your time.

-Neba