A lower-end Core i7, such as the 930, would be identical in performance to the 980X and you'd avoid the massive price premium they put on having an unlocked multiplier. In terms of hardware they are roughly equivalent (although "Extreme Edition" parts are generally binned higher than their regular equivalent).
A decent after market cooler and spending a few minutes overclocking would earn you comparable performance at a quarter of the price. The 980X won't "last" any longer than a regular i7 processor in terms of "future proofing".
I realize you have a large budget, but there is little reason to try and max that out at this time. I'd spend under $2000, and save the rest for an upgrade 2 or 3 years from now. You'll get more value for your money and you'll still end up with top-of-the-line performance.
