If you're spending that much, you'd want it to last... With DX12 around the corner, I'd really wait for the new gen. Especially since SLI/CrossFire is improving on the new gen AND with DX12, and the decrease in power requirement, for Polaris especially, it'll also be cheaper (cheaper PSU, less heat output, less noise).
For multiple cards, the new gen is definately worth waiting for.