Hi,
No matter what route you go (FSX, MSFS or XPlane) do bare in mind that none of these sims are plug-n-play so to say. While they would love to be PnP, there´s always some tweaking to be done and some hardware balancing. It is well known that you could have the best PC set-up in the world, but if you don´t know how to tweak, configure and know what order to install add-on´s etc. It will run like a turtle.
My guess is that you already know that from your Falcon days, but unfortunately it has not changed to much till date. Mind you my intent is not to discourage you, but you do need to do some homework still in todays sims. MSFS is less of a hasel then FSX, but still, as all of them, they need some care and if you want to get a true experience, you will need some 3rd. pary add-ons and be on top of things (updates etc.).
Yes, specs are a must if you want to get some help for sure
Iam sure the older memebers here are happy to see you back, so welcome back!