Future proof mobo or not? 750i, 780i or x38?

I am having trouble deciding what mobo to choose. With DDR3 coming and 45nm CPUs becoming mainstream, i am having trouble deciding which way to go. There are several variables involved: SLI vs xfire, DDR3 vs DDR2, socket 775 vs next socket. I am looking at spending less than $230, cheaper the better.

SLI vs xfire. I would like to get at least a 3870 or 8800GT. At this point it doesn't matter if i get ATI or Nvidia.

DDR3 vs DDR2. Before Christmas i bought 4G(2x2G) DDR2 800mhz. so i would like to keep it for a year or so. I would also prefer to let the price of DDR3 come down before i invest in it.

I will obviously stick with socket 775 for now.

Considering the rumors about Intel using a new socket next year and DDR3 being pushed on us, is there any reason to buy the most future proof mobo? If intel changes their socket, nothing is future proof. Should i get what i can afford, keep it for a couple of years and let all these changes take place.

for example. Should i get a good x38 or 780i mobo, so i can at least go with a 45nm CPU in the near future. Or should i spend less and get a 680i or a p35 and save some money and let all the new hardware come out. Will the 680i and p35 be good enough to last a couple of years.

I am thinking it is best to at least get a 45nm compatible mobo with PCIe 2.0 and DDR2 support. All that architecture should be supported for the next couple of years. I am thinking on the lines of a x38, 750i or 780i. The 750i is cheapest. The 780i is the priciest. The x38 seems to have the most flexibility.

What advice can any of you give?