What would be a good graphic care for i7 975@ 3.33Ghz and 16 GB RAM DDR3-1600?
I believe you’ll be flying into 2d mode - so an RTX 3060 or RX6600 would be a good starting point or even the GTX 1660 would be good. These would be minimum requirements I believe.
Ohh my, that’s from 2009. I had an i7-870 a couple years ago, and I don’t even think that generation of CPU supports PCIe 3.0.
The graphics card I had with it was a GTX 1060 3GB.
But, I never tried MSFS with that combination. I updated to a 10th gen i7 that was 9 generations newer 
before purchasing MSFS.
Personally, I would increase your Ram.
It should I have an i7-6 here and it has pcie 3 on it.
@op On this machine (when the network isnt hosed) I can get with everything set to ultra , and the lods set to 400 and 300, I get 25 fps when flying cross country, 18 in ny city, and for some reason, anywhere between 25 and 4 in cleveland, (again this issue seems to be more network issue since it just started happening recently). And this is on a 1080ti card that is 6 years old.
I have a gaming laptop with a 1660 in it, that is pretty much the same as the desktop and with everything set to ultra plus the lod tweaks it gets a pretty steady 30 fps.
Oh yeah I forgot to add in 4k…in 1080p the fps is like 34-45
Let’s make sure we’re on the same page here. The OP says he has an i7 975 @ 3.33GHz.
This is a first gen core processor from 2009. The Intel spec sheet doesn’t even list PCI-E for it, and it shows it supports up to 1066 MHz RAM.