I didn't realize by putting my Samsung 990 Pro (I know it's only Gen4) in the Gen5 nvme slot closest to the cpu, that it cuts the GPU lanes down to X8. My plan initially was to swap out the 990 Pro, with a Gen5 nvme drive when they came out, but judging by some of the early benchmarks I've seen, they're really only superior in terms on transfer speeds. Windows Boot and game loading sees no benefit. Would a 3080TI be limited by the X8 connection? I have 3 nvme drives I wish to use. The 990 Pro as my OS, one dedicated to games, and another for a video editing scratch disk. Would it perhaps be advisable to put the 990 Pro in the m.2_2 slot on the mobo, and then utilize the included ROG Hyper M.2 card in the very bottom PCIE slot, for the gaming drive and scratch disk?
Yes, don't use M.2_1 for a 4.0 drive. For a system 4.0 drive on boards which have 5.0 GPU lanes on a M.2 slot, always use the 4.0 slot that has the dedicated x4 storage lanes from the CPU. That's M.2_2 on your board. Additional storage should go through the chipset M.2 slots, leaving M.2_1 empty.
Personally, I would not bother with a 5.0 drive at all at the moment, as I'm not convinced the performance gain is all that useful for real usage (compared to the best of the 4.0 drives). The downsides of heat and the platforms not actually having 5.0 storage lanes (as far as either Intel or AMD are concerned) just make it not a good tradeoff. It's nice that ASUS and other board manufacturers give you a choice, but I'm not convinced based on what I've seen of 5.0 drives so far. I view the current platforms as really being 4.0 platforms that have a future-5.0 GPU slot (the GPUs are all 4.0 for now). The true 5.0 platforms will be some future generation (maybe soon, maybe not), not what we have today. 5.0 storage is a niche, but I just don't see it actually being all that worthwhile at present for general gaming/enthusiast use; there will be some cases where it does make a difference, but not for most.