Radeon 4670 = bad DX9 Lost Planet performance?

Hey, I've been playing Lost Planet with my Gigabyte 4670 1 GB DDR3, and it seems to struggle with Lost Planet in DX9 mode (I only have XP on my desktop). I've been playing the game at 1280 x 720, all max settings except AA and the card seems to struggle with the game at times despite the modest resolution, especially when there is motion blur. Is this in anyway synonymous with with ATi cards and DX9 performance with Lost Planet? Seems unusual that this card is experiencing worse performance than the 9800M GS in my laptop, despite every other game I have running much better on the Radeon 4670, though I must note that when I play on my laptop, it's on Vista and with Lost Planet it's in DX10 mode, not DX9, so there is that to think about I guess.

I would be very appreciative of any feedback on this strange performance issue. I do have the latest Catalyst drivers, and I even have my card overclocked to 800 MHz core speed and 900 MHz memory speed. And of course the mandatory posting of my desktop's specs:

Radeon 4670 1 GB DDR3 800 MHz core/900 MHz memory
AMD Athlon II x2 250 3.0 GHz
2 GB DDR3-1333
Windows XP SP3

It just seems so strange that despite the efficiency advantages of DX10 mode, that my Radeon 4670 would struggle in DX9 mode with LP so much at 720p no less (and that's pathetic!). Every other game DX9 game (or one with a DX9 mode to test) I've tested with the Radeon 4670 (including Crysis, Far Cry 2, BF2, BF2142, HL2 games, etc) takes higher resolutions so much better than the 9800M GS except Lost Planet, and I highly doubt it's the difference in memory transfer rate (9800M GS has a 256 bit memory bus, 4670 has a 128 bit memory bus), but I do suspect built in preference towards Nvidia graphics.

Once again, any feedback and experience as well as possible fixes would be extremely helpful and I thank you in advance! :D

:cry: No takers? It's so confounding!