Hi,
Yes 8 GB is definitely not overkill - After the last CRYPTO-CRUNCH when GPU’s were cheaper circa 2018 for my sins I got a GTX Titan X which is basically a jazzed up GTX 980 Ti but with 12 GB VRAM.
As far as MSFS goes the GTX 980 Ti is underneath the GTX 1080 Ti which were both top of the line cards only a few years ago.
How would a GTX Titan X do? - With the 12 GB VRAM - It’s gotta help a little - Please tell me it will - 
The reviewers at the time mentioned it was only 3% above a 980 Ti - But if all 12 GB could be used how much would this help? - Maybe not that much?