I have bought a number of pre-mined cards that range from doing okay to barely surpassing the base frequency. It's not like a temperature issue either, its just a silicon degraded so hard that the maximum voltage allowed gets it up to the base clocks.
I also mined a few cards for a year straight and they did show signs of slight degration to the maximum clock speed from before mining.
I ran mine at 75% though and 2 were completely water-cooled....
I'll take a chance on a mine card if it's like a fraction of the cost of another used card. So for 2080 Ti. $150 is the most I would pay.
That is the same symptom of a GTX 780 rev. 2 (GK110B type) that I have here. My brother purchased it for relatively cheap during the mining craze. In this card's case, it's not that it was mined, is that the previous owner ran it since 2014 without opening it for maintenance, for years on end at 90C load until it started crashing. It's purely a silicon degradation problem, it's just not designed for very-long-term high-stress situations like this.
The only solution I've found for it is to reduce its clock speeds to around 550 MHz. The card is fully functional then, but performs probably slower than your average GTX 580. Better than nothing, but disgusting regardless.
Still a bit early to call that one. There seems to be just as much concern over everything before 4xxx being made obsolete as there is over eliminating the large share of gaming market who decided to wait things out. The former coming to fruition among the very top AAA titles is considerably more likely than the latter. 9xx would be a more fitting place to hang the legacy hardware tag.
Ultimately it comes right down to what games OP will be playing. What requirements need to be met long term.
See it from my perspective: this is a 6-year-old architecture which was designed at a time where none of these new technologies existed and most weren't even planned. Sure, it was a great performer, and one may argue that it still holds... holds on what? DirectX 11 games? Then yeah. Get out of that comfort zone, and it'll go belly up.
The 900 series GPUs share practically all of the same limitations and are already "dead men walking". Their 8 years (NV's lifecycle policy) have already elapsed, and it's a matter of time until Nvidia disables Maxwell support on the drivers.
