Because the total PCIe bandwidth on the Z87 board is 16x, the 690 gets effectively run at 8x8x on that board but with PCie 3.0 full 16x bandwidth is rarely (never?) needed.
If the concern is strictly gaming with no more than two cards in SLI (or a single GTX690), I'll suggest the 4770k/Z87 combo as being a better value. In 3+ way SLI, the X79 would show it's worth (IMO)