Installed and testing now; it was a little fiddly at first, as I had a 3+3+2 power output, and had to clip open the cable tidys to get at the 2, and then I found there was a SATA port I was using behind where the 6600 sat (I checked the case/board size but didn't think to look at that, as the 970 didn't reach it) but fortunately had an L-shape SATA that would lay flat behind it... So far, the issues I had with hard lock ups are gone, so it seems it was definitely a very specific failing on the 970, but the old workhouse provided value for money over the years, and it's taking a well deserved rest now!
I'm still idly testing performance increase; the AMD software doesn't help much as it only makes suggestions, but it's unable to tell the difference between title screens and testing gameplay, so it keeps bouncing between the 3 ratings as FPS moves up and down. And the AMD "Raise Your Game" requires external software to claim, needs the card to be installed first, and gives only 2 games with this card (hardly worth £100+ as claimed), but one is Saints Row (which everyone who wants it will have a version of by now) and one isn't even released until next year. I was going to give them away, but I'm not sure I'll even get a simple Steam key if I try, bah humbug.
Still the card is silent and seems lovely so far, so I'm happy with it. Will give it a good working over in the coming weeks! Also the box came with a little bag of vegetarian Haribo, which was a miracle as of itself, you don't see gelatin free Haribo very often!