my thought is that you went this long with the 1080ti. this tells me you are not just chasing the latest greatest and fastest, but rather looking to get something that will last for your admittedly modest expectations.
the 6950xt will do what your 1080ti did for you. it will let you enjoy your games for a number of years. as gpu needs increase you're already ready for them for a good number of years.
so considering you don't expect 1000 fps at super ultra mega settings at max resolution, i'd look at the upgrade as simply assurance of being able to do your thing for years to come until you're ready for the 10,000 series from amd
i tend to do the same thing. i get more than i need for sure, but i know it will last more than a gen or 2 for my needs/expectations. what is "good enough" right now, may not be in a few years. where as what is "overkill" now will still be "good enough" a few years from now. if that makes sense.