That being said, you are spending ~$1000 on a CPU (assuming Canada), you've also spent a lot on a 4090 and (soon to be) 64GB of DDR5. I'm slightly confused why you are looking at value motherboards for such a system. I'd be inclined to suggest a X670E board, either a ROG Strix or AROUS Master or Taichi.
It's because CPU and GPU upgrades made a perfect sense for me, while I don't see why I should pay big money for a motherboard if I don't really get anything useful out of it. I hate paying big money if I don't see what it gets me, that's all. I have 12 cores now and need to have at least that many for work (web and graphic design, 4K video editing, 3D and MSFS airport design), and if I'm upgrading my PC that calls for 16 cores. And I'm a big fan of MSFS + VR (and built my own motion rig, custom pendular yoke, throttles, switchboxes etc.); it is so demanding that I could not even get a good experience with 5900X+3080. So I decided to upgrade and got 4090 when it was out - as 4080 didn't make any sense at all - too expensive for the performance gain it would have. It helped a lot, but it's clear that I'm CPU limited and this gives stutters, which in VR means an extremely nauseating experience. MSFS is probably the most beneficial 3D cash application. Not just for high FPS but the low 1% and stutters. I would have gotten a 5800X3D which simmers love if it wouldn't be a downgrade for my work. Can't justify paying money for a downgrade
So I kept my fingers crossed for AMD to release 16-core 3D cache CPU, and they did. Now it's the only one that makes any sense to upgrade to, in my very specific case at least. Unfortunately, it means new motherboard and RAM.
So I just want to get a decent motherboard that will work with 7950X3D, and let it work to the maximum of its performance (including PBO + CO overclock). I don't see why should I pay $200-300 extra if there are boards that apparently do everything I need without that premium. The fact that I'm already spending thousands on a PC doesn't change that. I still don't want to waste money. But maybe I'm not getting something? What ROG Strix or AORUS Master would give me that I need with 9750X3D? I don't care about gamer aesthetics, lights etc., nor for extreme overclocking (beyond PBO + CO), nor premium audio features (I use S/PDIF with a serious DENON amp and large floor-standing speakers and a sub for my sound, so it's digital passthrough anyway). I do have 3 M2 SSDs already + 2 SATA drives. So I see the point in X670.: board with 4 M2 slots is a plus (and 3 is a minimum with no room to expand). And so is S/PDIF - I can use USB audio interface if I have to, but it's easier to use optical out. Gen5 vs Gen4 - not sure, but I can see a little extra to be future-proof, I wouldn't pay a lot for Gen5 though as I don't need it any time soon.
ASRock X670E Pro RS has 5x M5 slots and S/PDIF, so I can justify +$30 over ASUS Prime-P (if ASROCK is OK as a brand), plus better VRMs as a bonus.
But paying extra $245 for a ROG STRIX - I don't see the point at all. I don't need ridiculously overbuilt VRMs that I'd never use, premium audio, blinken lights, more gen5 that Prime-P or Pro RS offer. Now, what is important is VRMs are enough for whatever OC is permitted on new X3D CPUs with modest headroom, that's why I have doubts about Prime-P that maybe some gurus here can clear or confirm.
