PC2-5400 DDR2 was recognized as 533mHz on Dell 8400

[Roybin]

I did not do many research before I jump to this DDR2 deal from newegg.
http://www.newegg.com/Product/Product.asp?Item=N82E16820145539
It is a CORSAIR XMS 1GB (2 x 512MB) 240-Pin DDR2 SDRAM Unbuffered DDR2 675 (PC2 5400) Dual Channel Kit.
After I bought it, I realized the Dell motherboard is very picky with the memory from some forums. Fortunately, the memory can be recognized as 533mhz(pc2-4200) on my Dell 8400 machine. When I try to oc the memory to 675mHz, I found that the Dell bios about memory can not be modified. The bios only showed memory is 533mHz. I searched many forums and try to figure out the relationship between my 800FSB and 533 or 675mHz memory. I was still very confused about that. It looks like pc2-3200(400mHz) is enough for 800 FSB.
ok, my questions are
1. are there any way I can set this memory to 675mHz on my dell 8400(intel i925x mb)?
2. which one is better choice? use this 1GB pc2-5400 which is down to 533mHz by my 8400, or use this 1GB pc2-5400 plus my old 512MB pc2-3200 which all run at lower 400mHz but larger memory 1.5GB?

sorry for the bad English. Thanks for your any suggestions.

 

[Twsmit]

Dells have a locked bios, you shouldnt have bought overclocker/fasterram than your system can handle if it was for a dell. i hope you didnt pay too much of a premium.

i would run the PC2-5400, dont drop any lower because your P4 could use the extra bandwidth.

 

[Roybin]

The price is similar as pc2-4200, only 71$ after rebate(free shipping). That is why I bought it so rashly .
Whatever, fortunately it can work at 533mhZ