Aurora R10, why x8 PCI slot for graphics card?

Because the heat in the SFF case will choke the speed before x16 ever would be the limiting factor.  It's the same with the R7-9, 11, if it helps to have good company. 

"The Aurora R8/R9 uses the Z370 Chipset that has 20 PCI Express Lanes Available.

The Aurora R11 uses the Z490 Chipset that has 24 PCI Express Lanes Available"

No, z370 (r7-9) has 24 chipset lanes.  But these are usually for slower speed items like usb, storage, sata, etc, not for running a GPU. That you would usually want to prioritize as a direct lane to the CPU, not a chipset lane.  This cpu lanes are in addition to chipset lanes. So total you usually have 40/44+ pcie lanes depending on cpu.

Some background from the Intel Site and Dell site:

The Aurora R8/R9 uses the Z370 Chipset that has 20 PCI Express Lanes Available.

The Aurora R11 uses the Z490 Chipset that has 24 PCI Express Lanes Available,

In R8/R9/R11, 2 graphics cards running at x16 exceeds the available PCI Express Lanes.

Specifically for the R11 - from the service manual and advertising material - Slot 1 (PCIx16) uses x8 lanes, Slot 2 (PCIx4) uses x4 lanes, Slot 3 (PCIx4) uses x2 lanes and Slot 4 (PCIx16) uses x8 lanes.  This leaves 2 extra lanes which I don't know why they aren't being used unless they use those lanes to connect directly to the CPU.

Also, from another thread and off topic, most of the M.2 nvME SSDs require 4 lanes to achieve rated speed.  The M.2 lanes are connected directly to the CPU so they don't pull from the available chipset lane total.  To add the second M.2 SSD using an adapter card and achieve the rated speed requires using Slot 4 as Slot 2 is blocked by the graphics card and Slot 3 only provides 2 lanes, essentially giving up the 2'nd graphics card or running the adapter driven SSD at half of its rated speed.

From the Aurora R11 Setup Guide:

@sm56 :

How did you end up getting things upside down? Should have been this way:

Dell Aurora --> r/buildapc

You'll find that your ROG motherboard will run circles around your Dell.

@sm56 :

Feeling old and only want to build 1 machine every few years these days and it was for my wife's birthday..

Paging @Anonymous . Why some people feel old and build countless (2) machines?

As long as you're happy, it's all good. Enjoy!

I have built PC's since the early 90's.... Built my wife up a nice one but wanted to get another Alienware which is the Aurora R10 Ryzen edition with Ryzen 3800X 8c/16t CPU, 32GB Hyperfury 3200 memory, RTX 2080ti and m.2 nvme 2tb stick drive ...

I have an Aurora R4 sitting next to my R10 and have had the R4 8 years now with hardly any problems although I have upgraded the Aurora R4 graphics card to an EVGA 1080ti replaced the old I-7 3820 cpu with an I-7 4930k and upgraded the memory to g.skill DDR3 32 GB, bought an nvme m.2 pci adaptor and Samsung 970 EVO M.2 NVME and installed in one of the open pci slots of the R4.... and was (and still is) a good system that served me well and that I continue to occasionally use.

For the most part I am happy with my NEW Alienware Aurora R10... It seems to be a little zippy and fast machine... just a few oddities that I have question about like x8 pci for graphics instead of the standard x16.... and some bloatware like DellDataVault that I disabled because it was eating resources...

Feeling old and only want to build 1 machine every few years these days and it was for my wife's birthday.. and like I said, for the most part I like Alienware!!!   

The Intel CPU (i9 10900KF) has a max of 16 PCIe lanes.  If all 16 were allocated to the GPU then there were be a performance hit across the PCIe bus.  Even so, the GPU performance difference between x8 and x16 is so small as to be insignificant. 

https://www.gamersnexus.net/guides/2488-pci-e-3-x8-vs-x16-performance-impact-on-gpus

If I am not mistaken, the GPU uses only the CPU's PCIe lanes and not the chipset's. Is this correct?

Well if we can ever get Nvidia 30xx gpu's that will fit in the R10 using pcie 4.0 on x8 on the b550a then I guess that would be the same speed as pcie 3.0 x16

I think you are correct that current games see little benefit between x8 and x16... But who knows what it will be like 5 years down the road...

P.S.

I remember 5+ years ago some saying that ram speed does not really matter but these days a lot of people are, if not overclocking their ram, using xmp profiles to get the most out of it since cpu's these days can chomp thru more data with more cores than they did back then, making ram speeds more important today.

@Kyzyl_Tuva, Just stumbled on this thread but Yes, I think the Ryzen R10 motherboard service manual indicates a B550A chipset and thus, have one 16x PCIe G4 capable slot (shown as a light blue PCIe slot on the PCB). AMD's B550 chipset architecture diagrams confirms a single 16x PCIe G4 capable slot hanging off the CPU complex.

I think the OP, @sm56 asked this a long while ago... It seems there may have been some confusion a few months back.