Problems Populating 3 DIMMs on ASUS K8V-X

I have an ASUS K8V-X which has 3 DIMM sockets. 'been using 2 sticks of 512 DDR400 PC3200 memory--and everything benchmarks accordingly.

Added a 3rd 1gig DIMM so my RAM looks like:
DIMM1: Corsair VS512MB400 512 MB PC3200 DDR SDRAM (2.5-3-3-8 @ 200 MHz)
DIMM2: Corsair VS512MB400 512 MB PC3200 DDR SDRAM (2.5-3-3-8 @ 200 MHz)
DIMM3: Corsair VS1GB400C3 1 GB PC3200 DDR SDRAM (3.0-3-3-8 @ 200 MHz)

The Problem:
That ASUS mobo overides the Explicit BIOS setting MEMCLOC set to DDR400 and defaults the Memory Bus to 100mhz (i.e, cuts it in half)---Apparently a fail-safe value it tries when it thinks there's a memory issue. I haven't found any way to force a 1:1 CPU/MEM ratio.

I'm not sure if this is a deficiency in my ASUS mobo's design or something I'd see in any AMD mobo configured this way?
ALSO
I'm now hearing from a lot of folks that they've had issues populating these 3 DIMM mobo's even with 3 sticks of identical DIMMS---so I'm checking this forum out for feedback before I RMA my 1Gig DIMM and buy a 512 DIMM identical to the 2 512's I already have.

[Tyler]

Yeah to me it just sounds like your motherboard is not capable of that. It seems a lot of motherboards get touchy when mixing RAM.

Have you tried putting the 1GB in DIMM1 and the others in DIMM2/3?

Hi Tyler,
Thanks for answering. Yes I've tried most of the obvious stuff.

I've gotten no real response from ASUS's Forum but the Tech Staff at Corair's Forum, as usual, have been most helpful. And they're basically saying what you are:
Mixing DIMM sizes (especially when all this RAMM is Double Sided) on this (and most other) mobo's is generally not your shortest road to happiness :-) Corsair's Ram Guy also suggests that with these 3 DIMM mobo almost the only way to go 2GIG at full SPD spped is with 2 1Gig DIMMs--and I think he's right.

He also verified for me that typically my mobo, many mobo's, especally Socket 754 mobo's WILL indeed drop the RAM BUS to 100MHz (DDR200/PC1600) when it's confounded.