NVME / SSD compatability or suggestion question

I have a Gaming/VR PC that I put together a couple of years ago which consists of Intel i7 4790k CPU, GTX 1070, 16GB of RAM, a 3 SATA 3 SSD drives and a couple of SATA 3 HDs on an ASRock Z97 Extreme6 mobo.

I've run out of space on the SSDs and I need to purchase another 0.5-1TB SSD but I'm not sure what makes the most sense due to the limited bus lanes available in that architecture. The board has one "Ultra M.2" socket which supports M.2 PCI Express module up to Gen3 x4 (32Gb/s) and another M.2 socket that supports SATA3 or PCI Express module up to Gen2 x2 (10Gb/s).

Mobo manual says that if I use the Ultra M.2 port than the PCI port which the GTX1070 is plugged into will drop down from 16x to 8x. I tried to research to see if this has any real-world impact and read conflicting results so I'm a little concerned as I may want to upgrade the graphics card at some point for improved VR and potential 4k gaming. Also, I'm not sure if this architecture can fully utilize the speed of something like a Samsung 960 EVO NVMe or if I'm better with sticking to regular M.2 or SATA3 solution.

Any thoughts or recommendations? Much thanks.

I haven't seen any PCIe lane scaling testing on the 1070 but NVIDIA GeForce GTX 1080 PCI-Express Scaling | TechPowerUp has benches for the 1080. There is some fps loss in certain games - this performance loss will likely be smaller on the 1070 since it's pushing less data over the bus.

I would personally stick with SATA over losing GPU PCIe lanes. NVMe would really only help load times - I haven't been bothered by load times in a very long time.

On a single 1070 I don't think you would ever notice the difference between 8x and 16x for the pcie lanes.

I also doubt you would notice the difference between a sata ssd and an nvme drive.

You really can't go wrong either way here I think. I would just look for the best deal on the size of drive you think you need and go with that, be it sata or nvme.

Hi,
Depending on exactly where the M.2 port is you might also need a heat sink for the 960 so it would add a little more to the costs over a simple sata ssd
Benchmarks like 960's but that's about it.
I'd just stick with a good old 1tb 850 pro or evo
New Sansung 860's are out and the stat's are pretty darn close to the 850's just a hair better.

Thanks all, based on your responses I'll pick up either a M.2 SATA or PCI Express (Gen2 x2) SSD drive to avoid the price premium of NVMe and any potential GPU bottleneck.