Right, so I'm not a low-level PC hardware expert or anything, but:

We only got resizable BAR like a couple of years ago, and it was very much a premium enthusiast feature at the time. Are modern engines and the games built for them optimised to expect resizable BAR as a baseline yet? If not that will still be a limiting factor right?

I thought the reason resizable BAR was introduced was because we hit the limits of what the previous approach allowed regardless of the speed of the link

i.e. of course it doesn't make a difference with games today, they're built targeting hardware configurations that will limit the utility of extra storage bandwidth

Reiterating that I might have this entirely wrong, so I'm more than happy to be corrected here