I believe I've been asked to do video on a few products malfunctioning the past few years (quest 2, vega64, and maybe another I can't remember)
Seems to be becoming the norm.
ti4600 had good gains, 9700pro gave fairly large increases with overclocking, so did the 5900xt, x1900AIW gave very large gains in terms of performance, hd4870 had a fair amount IIRC, 8800gt had monstrous head room, gtx460 had huge head room, hd7870 had massive headroom along with the hd7970...