Mobo and GPU

Hello!

I'm building a new gaming computer, but I need some help choosing motherboard and GPU. Here's what I've got so far:

CPU: Inte Core 2 Duo E8400 3,0GHz

RAM: Corsair XMS2 DHX TwinX DDR2 PC6400/800MHz CL4 2x2GB

PSU: Corsair CMPSU-650VXEU 650W

HDD: Western Digital Caviar SE16 WD5000AAKS 16MB 500GB

OS: Windows Vista Home Premium 64-bit

Case: Antec 900.


I play in 1280*1024 at the moment, and I'd love to have a computer that could play at best settings for that resolution, and possibly higher. I'm also planning on overclocking the CPU and GPU (RAM and mobo too if needed).


The "problem" with the mobo and GPU is this: I've got a friend who works in a warehouse where employees (=him=>me) can get stuff they got there really cheap. They do not have everything though, and the GPUs and mobos of interest they've got are these:

GPU: PowerColor ATI HD3870 (~$120); LeadTek/Asus 8800GT (~$130).
Mobo: Asus Maximus Formula (~$150); Asus P5E (~125); Asus P5K (~$65); Asus P5K Pro (~$75).


The question is therefore how to use the cheap stuff for the best. I can spend ~$450 on GPU and mobo. Here are some ideas:

1. Go with Maximus Formula or P5E and a Crossfire configuration of 2 HD3870. That'd be about $350-$390.

2. Buy an SLI board, and do SLI with 2 8800GT. Are there any good SLI boards for ~$150?

3. Buy another card, for example 8800GTS or 9800GTX and do one of the P5K-boards.

What do you think? Tell me if you'd change anything on the rest of the build as well. Nothing's bought yet.