Can't decide on Z370 board...

I usually buy Asus board, but none of them really look interesting...

I'm looking for:
Dual Intel NIC
none of that killer nic bullshit
10gb nic would be nice
heatsink for m.2 would be nice
thunderbolt support, either onboard or add-on card
good OCer

on the asrock pro gaming i7

it says:

3 x PCI Express 3.0 x16 Slots (PCIE2/PCIE4/PCIE5: single at x16 (PCIE2); dual at x8 (PCIE2) / x8 (PCIE4); triple at x8 (PCIE2) / x4 (PCIE4) / x4 (PCIE5))*

if I plug in a thunderbolt 3 card into PCIE5 (its 4x card), will that slow down my PCIE2 16x?