Looking for a Mobo and GPU...maybe

first off, here is the build that i thought i settled on
http://secure.newegg.com/WishList/ [...] tTitle=new
now my initial intention was to crossfire two 4870s running on that 22" 1680x1050 and occasionally my 42" plasma that is 1024x1024 (1080i, 720p). now what others have told me is at those resolutions, crossfire would be a "waste". i was debating on whether or not the price of the x16/x16 of the X48 board would be worth it over the x8/x8 of a P45. but since it would be a waste i guess all of that goes out of the window. so now im just looking for GPU that is under $300 and a mobo that will be good enough for what i want to run.

am i crazy for going back and forth on this decision or is my original build pretty solid? i guess what im trying to figure out is where i can cut some costs and ive targeted the motherboard. id still like to crossfire and i could drop ~$100 if i went with a P45 but would the x8/x8 in crossfire not be THAT great compared to x16/x16? ive seen some benchmarks and at higher resolutions the difference seems to be around 10-15 fps. but at the same time x16/x16 would be more "future proof" if you will. so what do you guys think? someone educate me please!

ahh sorry i should have stated the reason why the case, psu, hdd, and dvd drive arent there. its because i have them already this is all going into an Antec 900 with a corsair 520w modular psu. and you were spot on about crossfiring in the future, that was my intention all along. maybe a year or so down the road ill pick up another 4870 and a new psu. but i am not looking to run crossfire as of right this instant. and yes i do plan on overclocking but not much. which P45 would you recommend? also, what if i were to use a resolution of 1920x1200? would the advantages of crossfire show more at that resolution? sorry im pretty clueless about these things but i have a choice between a samsung 22" and a 24" soyo which is the 1920x1200 one.