I have an Asus Z790 Apex Encore with an 14900K.
As I understand I have to choose between my RTX4090 running at 16X PCIE4 (in the PCIE5 slot)
or my PCIE5 SSD running 4x PCIE5 and my RTX4090 at 8x PCIE4?
I can still return my PCIE5 SSD (Corsair MP700) or my PCIE4 SSD (Samsung 990 Pro).
I've read that the performance loss regaring the RTX4090 is only 1-2% when running 8X PCIE4, however in real world life will I ever see the difference between my Corsair MP700 PCIE5 SSD and my Samsung 990 Pro PCIE4 SSD?
Also I was wondering for future upgrades, will those graphic cards be 8X PCIE5 or 16X PCIE5?
If 8X I would be able to run both at PCIE5 speeds? Or am I thinking wrong here?
Any advice welcome
Not familiar with your board and what situations will result in 8x, but you're right, the difference in performance between x8 and x16 is minimal and you'll never notice. I've read that the difference is more like 4%, but I guess it depends on the board and your GPU.
The 4090 and the Gen 5 SSD should both be future proof for a good while yet.
In terms of your SSD speed, you're only going to notice if moving a lot of data and that probably won't be very often. I do move a lot of data during backups - sometimes a few hundred GB, but quite honestly I feel no need for Gen 5. I'm very happy with gen 4 speeds at the moment.
So overall, it's just down to choice - you'll get great performance whatever priority is best for your situation - GPU for gaming vs. fastest data storage. As you already have the Gen 5 SSD, I'd be tempted to keep it and then you'll get more benefit when you eventually get a board that can fully support both at the same time.