Which PCI slot to use with Gen 5 m.2 and 4090 GPU in ROG Maximus Hero

[Beldins]

Here is the issue.  From what I understand if I plug a gen 5 m.2 drive and a 4090 GPU in the primary slots they will share PCI lanes which will reduce performance. 

I think the 4090 GPU is gen 4 so it seems right to me to use the gen 4 slot for the GPU at the bottom of the motherboard and keep the gen 5 m.2 drive as in the primary slot.  But will this mean they both have all the lanes they need or its not going to make a difference either way and I just have to accept that there is only 20 lanes to use in total.  

Am I over thinking this or am I right

What is your recommendation. 

[VRT]

The problem with the Z790 boards is that the GPU slot and gen 5 m.2 slot share the same bandwidth. If you put the an m.2 drive in the gen 5 slot this means your GPU will be running at x8 no matter what speed you choose for the PCI-E slot (3.0, 4.0 etc). In real world performance gen 4.0 x8 is slightly better than 3.0 x16, and it only means you will lose 2-3% of your performance against 4.0 x16 for your GPU, so if you can deal with that minor loss to the performance then go for it.