So... that Nitro card I bought. Turns out the coil whine wasn't the card at all. Neither was the fan noise. Oops
Fan noise was my case fans, which it turns out are actually quite loud when they ramp up. I didn't know this previously, as the blower XT kept case (and therefore CPU, which is what the fan speed is tied to) temps low. But swap the blower card for one that dumps all of the heat in to the case and... boom, problems. I discovered this before I boxed the card back up. The CPU was running 10°C warmer, with fans at 1150 RPM rather than 600 RPM.
And the coil whine? That persisted after swapping back to the Reference card, and has been bugging me for days. I've just found the source; the POS broken LG monitor I bought off the classifieds last year. So now not only does it have dozens of dead pixels, it now serenades me with it's awful whiney song the entire time I'm at the PC.
So aside from the bent PCI bracket, the Nitro+ was fine. I just needed better case fans and maybe a better case.