I just purchased an ASUS P7P55D-E LGA 1156 Motherboard and just found out that the 1 x PCIe 2.0 x16 slot and 1 x PCIe 2.0 x16 (@x4 mode electrical) is not ideal for a dual gpu setup in terms of performance. Right now I only have one ATI 5870, but in next few years I was planning on just picking up another to keep up with gaming performance. The next ASUS mobo, the ASUS P7P55D-E PRO LGA 1156, features 2x PCIe 2.0 x16 lanes (single at x16 or dual at x8 / x8 mode). I've read that the difference between x16 and x8 is not noticable and thus good for Crossfire.
My question: Is it worth the extra $50 to get the x8/x8 mode for a 5780 Crossfire setup in 3-4 years or would I be better off scraping the dual gpu idea and buying a new single GPU at that time?