Actually, the only way to get x16 x16 on a z97/z87 motherboard is through the use of a PLX chip, which is almost always SLOWER for 2 card setups! PCIe 3.0 x 8 is absolutely heaps of bandwidth for any graphics card. While going to 16 lanes gives the card more bandwidth, it requires the PLX chip which introduces latency and benchmarks consistently show a (very small) decrease in performance.
Now if you wanna go 3 or 4 way SLI on Z87/Z97 you've go no choice but to go with a PLX mobo, but for two card setups it's worse! Don't do it?
OP, maybe you could describe in a bit more detail what the problem you're trying to solve is? It'd be real shame to spend all that money on a new motherboard to get no improvement, or even slightly worse performance. And I think that's exactly where you're heading at the moment.