RTX 3090 or 3090 Ti, or RTX 4080/4090 if you do not mind the price.  This case can support a triple card width high power gpu.  Liquid cooling of gpu would be a plus, or add more front intake fans (default is two 120 mm fan).

3090/4090 will be bottlenecked by cpu but they have better future proof if you plan to upgrade the whole pc in a few years.

https://www.userbenchmark.com/System/Alienware-Area-51-R5/67859

R4 R5 have x299 chipset lga2066 socket (R2 has x99 chipset lga2011 socket)

https://www.hardware-corner.net/compare/Alienware-Area-51-R5_vs_Alienware-Area-51-R4/

I am not seeing any CPU sockets referenced in that link. I do see an Intel Gen 10 processor referenced . . . which I know is wrong.

That's great news! Is it worthwhile to look at lesser GPUs that are not as expensive as the 3090 and 4080/4090 series? I reviewed some Black Friday deals on 3090's, still about $1000 and up. 

Perhaps I can also swing in a liquid cooling card into the 3rd slot? I saw a few of those too that fit GPU slots. Interesting kit indeed.

3080 for gaming.  no need to consider 3080 ti.  Some reviewer seem to say 3090 is too good for gaming, you do not need it, and it is for artists and game developers.  https://m.youtube.com/watch?v=Vtkk-_0jrPU

another reviewer said about 3090 ti “it’s massively overkill for gaming. It’s really a hybrid GPU, thanks to its goliath 24GB of VRAM. This means it’s best suited by content creation, 3D rendering, and other professional workflows.”

I am not suggesting that eBay sellers are the definitive source for information . . . but over the years,  the large number of Area 51 R5 motherboards listed as LGA2011 gives the notion some credence.

I am leaning towards a 3080, definitely. I might see if I can somehow sell my gently used 1080's afterwards, since surprisingly, they are still worth some nice coin too.

No . . . this would not cause an issue with updating your graphics card. The issue is whether or not your CPU is causing a bottleneck for your graphics card. That would depend upon what CPU you have . . . and to what graphics card you choose to upgrade.

You can use CPU-Z to see your CPU version and motherboard socket.

So, are you suggesting this will definitively cause an issue with upgrading the GPU? Since the MB is very accessible, is there a part number to verify what type it is?

Only be good for 4K. Any lower resolution and you will get a bottleneck, especially at 1080P.

In my opinion, while those systems were great a handful of years ago, they are not worth upgrading to previous or second generation of video cards.

Technology moves too fast and by the time you upgraded all the components you could have had better performance if you would have gotten a new system.

In my opinion not worth the upgrade if you are looking for more performance.

I guess it depends on your usage regime . . . and how much that small bottleneck at 1440p matters for your intended purposes.

Also depends on RAM. Older systems will typically have slower speed RAM. Than you factor in the other limitations of a board from that era, and upgrading for performance starts to make less and less sense when compared to an average gaming configuration of today. Especially with black Friday sales in full swing.

Absolutely true if you are trying to keep up with the latest gaming frenzy. Not everyone uses their computer as a toy to play games. My Area-51 R5 is a work-from-home rig that is used to run petroleum engineering programs, reserves & economics software, Spotfire, MS Office apps. With 64GB 3200 MHz RAM, 18 core processor, and the slightly bottle-necked RTX 3080 it is much more than adequate for all of my purposes . . . plus it was fun to build!

Re: surprisingly, they are still worth some nice coin too.

GTX 1080 used to be a king pin of GTX series, that is before RTX came along.

Re: MSFS lagging issue

a rtx 2080 or above will do well w A51 R5 cpu i7-9800x (R4 bios limits cpu to 7000 series)

Microsoft Flight Simulator Ideal System Requirements: