pcie 3 x16 vs x8 for AMD 7900XTX

[76561198095142420]

Currently I have a GTX 1080 which is about 280 mm and fits in the first slot of my mobo Asus z490e. I am getting 7900XTX but there is not enough clearance in my case (Ultra Modded Q500L) because of the PSU. Wondering if running this bad boy in x8 pcie 3 is going to make a difference? I don't see any difference at 4k for gtx 1080.
Option 2 is to maybe get a pcie riser cable but I doubt the card will align in the case because it has to go in the pcie slot.

[Bing Chilling]

your motherboard doesn't have pcie 3.0 16x??
what motherboard are you using?

also 8x pcie 3.0 could cause abit of performance loss for such a high end card
pcie 3.0 8x is on par with pcie 2.0 16x
https://www.youtube.com/watch?v=9iEKZ8HXPvw
this isn't your exact card but is still 7000 series. the loss will be about 8-15% at 1080p and about 5-10% at 1440p same with 4k

[Bing Chilling]

as a quick follow up i didn't notice you did put your mobo in your description.
you have a pcie 3.0 16x not 8x so the performance loss would be within 2-5% at all resolutions.

https://rog.asus.com/ca-en/motherboards/rog-strix/rog-strix-z490-e-gaming-model/

[76561198095142420]

the issue is that I am going to put it in the second slot which is x8

[Bad 💀 Motha]

GTX 1080 Ti even, only needs PCIE 3.0 X8-X16

However 7900 XTX MUST be used on a PCIE 4.0 Motherboard + CPU; otherwise it will run at either X4 or X8 on PCIE 3.0; THIS will handicap such a GPU, as it really needs X8-X16 on PCIE 4.0 to open up its performance and usage; just like a RTX 4080 or 4090

What you will end up with is an expensive power-horse of a GPU that will now max out at 40-50% usage.

[Bing Chilling]

that mobo has 3 slots. the top 2 have pcie 3 16x then the very last one has 8x
(the two with silver outlines around the pcie are both 3.0 16x)

does the gpu really not fit in the second slot? but does in the last.. ?

[Bing Chilling]

Originally posted by Bad 💀 Motha:

GTX 1080 Ti even, only needs PCIE 3.0 X8-X16

However 7900 XTX MUST be used on a PCIE 4.0 Motherboard + CPU; otherwise it will run at either X4 or X8 on PCIE 3.0; THIS will handicap such a GPU, as it really needs X8-X16 on PCIE 4.0 to open up its performance and usage; just like a RTX 4080 or 4090

really?
https://www.youtube.com/watch?v=v2SuyiHs-O4

[Bad 💀 Motha]

And why can't you use PCIE X16 length #1 or #2 slots?
X16 length #1 is top
X16 length #2 is middle

Either of these should work. How can your PSU be in the way? As it should be at the bottom of the Case below the entire Motherboard.

Originally posted by Bing Chilling:

Originally posted by Bad 💀 Motha:

GTX 1080 Ti even, only needs PCIE 3.0 X8-X16

However 7900 XTX MUST be used on a PCIE 4.0 Motherboard + CPU; otherwise it will run at either X4 or X8 on PCIE 3.0; THIS will handicap such a GPU, as it really needs X8-X16 on PCIE 4.0 to open up its performance and usage; just like a RTX 4080 or 4090

really?
https://www.youtube.com/watch?v=v2SuyiHs-O4

Here's the problem; NVIDIA GPUs can be used an older Motherboards such as PCIE 2.0 and 3.0; AMD basically can not. It does work but it would force that GPU to run @ X4 speeds/bandwidth, which is not enough. AMD has the modern GPUs function like that by design.

[Bing Chilling]

im also confused how the bottom one apparently fits but not the middle or top

[Bing Chilling]

Originally posted by Bad 💀 Motha:

Here's the problem; NVIDIA GPUs can be used an older Motherboards such as PCIE 2.0 and 3.0; AMD basically can not. It does work but it would force that GPU to run @ X4 speeds/bandwidth, which is not enough. AMD has the modern GPUs function like that by design.

huh never knew that, that said i've only ever had one amd gpu (r7 250 gddr3) back in like 2012 then nvidia the rest of the way. good to know i suppose.

[Bad 💀 Motha]

Yes it's funny because there are probably hundreds of videos showing that say RTX 30 or 40 series doesn't NEED to be in a PCIE 4.0 or 5.0 slot; but how many videos go into depth on that matter when it comes to modern Radeon GPUs...

Chances are, if you have to work the situation to where you're seeing yourself installing a modern high end GPU like 7900 XTX into even a PCIE 3.0 Motherboard; then chances are your CPU is not even remotely close to good enough and would be a sore bottleneck with the GPU anyways. So even if it does work out for you hardware function wise, you're going to have a GPU handicapped by a old CPU + MOBO and be lucky to get HALF the GPU performance you should be getting on a modern CPU + MOBO.

It would be like pairing a Intel 9900K + RTX 4090 together; it's going to be an expensive joke.

[76561198095142420]

it is because of the power supply. Corsair RM1000. It is a full atx build in a modded cooler master q500L case

[Bing Chilling]

Originally posted by Teammates quit 2% slower:

it is because of the power supply. Corsair RM1000. It is a full atx build in a modded cooler master q500L case

the psu in that case goes in the bottom right no? so how is the gpu gonna fit on the bottom slot? this makes no sense lol

[Bad 💀 Motha]

Originally posted by Teammates quit 2% slower:

it is because of the power supply. Corsair RM1000. It is a full atx build in a modded cooler master q500L case

That's going to run way too hot; as it lacks proper airflow for such a config.

At the very least the GPU should fit properly when using the MIDDLE PCIE X16 slot.

If not then what you need is also a different Case.

[Bing Chilling]

Originally posted by Bad 💀 Motha:

Originally posted by Bing Chilling:

the psu in that case goes in the bottom right no? so how is the gpu gonna fit on the bottom slot? this makes no sense lol

No the PSU mounts in a really dumb way Front + Top, with all the cables pointing down.

looking at the website, it mounts at the top right? behind that little piece of metal?
that has to be the strangest psu mount i've ever seen.

[Bad 💀 Motha]

Originally posted by Bing Chilling:

Originally posted by Bad 💀 Motha:

No the PSU mounts in a really dumb way Front + Top, with all the cables pointing down.

looking at the website, it mounts at the top right? behind that little piece of metal?
that has to be the strangest psu mount i've ever seen.

Yes it's a unique design with space saving in mind. It's meant for people who want the side of the case to act as the front. Notice where the Front Ports are.