Question Z790 Gen 5 shared bandwidth / X670E a better choice?

[Syed117]

Haven't built a gaming pc in 6 years and it's about time.

Current in shambles plan is the rog Z790 extreme / 13900k / aorus gen 5 10000 / 4090. Already have the 4090 and just ordered that gen 5 M2 which is expected around the end of this month.

Here's the issue:

The gen 5 M2 has to go in the m2_1 slot because that's onboard and the 4090 is too large to make use of the expansion card in the lower PCIE slot. Mobo manual also says to put gen 5 M2 in the m2_1 slot. The manual makes it seem like with the 4090 in slot, it will run at 8x and the gen 5 M2_1 will run at 4x.

That can't be right, can it?

Do I have to ditch this plan and go X670E and use the gen 5 M2?

And yes I know this first gen 5 M2 will probably suck and there might not be any real difference until the drives mature and all that.

 

[Lutfij]

What's preventing you from removing the heatsink off the SSD that comes bundled with the drive and the using the motherboard's heatsink to cool said SSD.

And yes I know this first gen 5 M2 will probably suck and there might not be any real difference until the drives mature and all that.
You probably answered you own question there.

 

[Eximo]

Yes, the typical Z790 layout is to share bandwidth between the main x16 slot and the first gen 5 M.2.

X670E is a better design in that regard since they dedicate 4x lanes from the start.

The better question is, why do you need a gen 5 M.2?

 

[Syed117]

The better question is, why do you need a gen 5 M.2?

I'll be honest. It's the shiny new thing and I can't help myself. Even if I know it's not the best move.

What's preventing you from removing the heatsink off the SSD that comes bundled with the drive and the using the motherboard's heatsink to cool said SSD.

And yes I know this first gen 5 M2 will probably suck and there might not be any real difference until the drives mature and all that.
You probably answered you own question there.

Definitely would remove the heatsink and use the one that comes with the board. Just worried about the bandwidth splitting and how much performance would be lost because of it.

 

[Eximo]

As of right now, practically none.

I've seen a few people running at PCIe 4.0 8x and 4090 don't even seem to notice.

So 5.0 8x is going to be twice that when they get around to making capable GPUs, so that shouldn't be a problem.

PCIe 6.0 will probably be available by the time it matters.

 

[Syed117]

As of right now, practically none.

I've seen a few people running at PCIe 4.0 8x and 4090 don't even seem to notice.

So 5.0 8x is going to be twice that when they get around to making capable GPUs, so that shouldn't be a problem.

PCIe 6.0 will probably be available by the time it matters.

Yeah, I would guess so.

Here's the main issue. Doesn't this make it look like if I put the 4090 in in the x16_1, the m.2_1(gen 5 m2) would run at 4x?

 

[hotaru.hino]

https://www.techpowerup.com/review/nvidia-geforce-rtx-4090-pci-express-scaling/28.html

Even a 4090 sees maybe like 3% loss if going from PCIe 4.0 x16 to PCIe 4.0 x8. Even if you drop down to PCIe 4.0 x4 or the equivalent, it still won't drop below 90% relative performance.

 

[Eximo]

4x is the max for M.2.
the x16 slot would still have 8x lanes. 4x lanes would just disappear and your second x16 slot won't be operational at all. (Not sure why it couldn't still be 4x, but that isn't what they did)

I would just install the drives in the 4.0 slots and call it a day. Even the 5.0 drive.

I'm running a 4.0 in a 3.0 M.2 slot, I notice nothing. It could be faster, but for what I do we talking seconds of load time, if that.

 

[Syed117]

4x is the max for M.2.
the x16 slot would still have 8x lanes. 4x lanes would just disappear and your second x16 slot won't be operational at all. (Not sure why it couldn't still be 4x, but that isn't what they did)

I would just install the drives in the 4.0 slots and call it a day. Even the 5.0 drive.

I'm running a 4.0 in a 3.0 M.2 slot, I notice nothing. It could be faster, but for what I do we talking seconds of load time, if that.

Alright, so after all this. I'm find this:

Z790 scenario
4090 will run x8
gen 5 M2 will run x4
other M2 will run x4

X670E scenario
4090 will run x16
gen 5 M2 will run X4
Adding more m2 drives will cause the 4090 to run at 8x.

At the end, the 4090 seems destined to run at x8 since I will have more than one M2 drive. I guess it's fine going either way.

Thank you. I appreciate it.