I'd go for the X38 if you want to Crossfire since P35's have one 16x electrical slot and one 4x electrical slot for two cards, and the PCI-E 16x slot that runs at 4x electrical will slow down even 3850's in Crossfire. For just one graphic's card, get a P35 for sure.
About DDR2/DDR3 boards, as far as I know the only con there is that it limits how many sticks of memory you can install. It looks like on that Foxconn you can have 4 sticks of DDR2 totalling 8GB or 2 sticks of DDR3 totally 4GB. That doesn't sound bad to me at all, unless there's some sort of performance hit taken when a board supports two typs of memory? (of course as long as you aren't using both types at the same time )