Or else there's a sale on
2x XFX HD-575X-ZNFC Radeon HD 5750 1GB 128-bit GDDR5 PCI Express 2.0 x16 HDCP Ready CrossFireX Support Video Card for $255
1x Sapphire Radeon HD 5770 1GB 128-bit GDDR5 HDCP Ready CrossFireX Support Video Card
w/ Free 4GB Flash Drive for 155
Or should I save and do one of these Crossfire configs?
EVGA E758 is a premium motherboard and quite expensive if you will never put three graphics cards in it. The classified is only necessary for 4 graphics cards. The motherboard is just not that important of a component to take valuable budget away from more important components (like the GPU).
Crossfire is really not a good thing, you should try to avoid it unless you cant. A single more powerful GPU is always better unless there is a strange pricing situation or no such GPU exists.
At your budget the ASRock x58 extreme or a Gigabyte/ASUS x58 motherboard in the $200 ballpark would make alot more sense.
Its hard to argue against that free PSU. ITs not a great PSU, but its OK. With that 600W PSU you are only going to run one 5870 so you dont need an expensive 3 GPU motherboard.