Growing up fishing Erie, 7" was our bare minimum keeping size if it was a slower day. On the good days, I'd like to second Dr. Bill's 8-12", though perch over 12" in the Western Basin of Erie were a rarity.
In my experience with walleye, the bigger they are, the greater the "fishy" taste, although butterflying helps with walleye. I've not had experience eating pond raised perch (will compare this fall when I cull a few), but years ago I had a rural barber (I mention this for when we get to the feed part) that raised perch in tanks to then fillet out and eat. He said they tasted horrible. That being said, I would bet money that he was likely feeding dog food as he was very rural and this was years (20+) ago. Furthermore, who knows the quality of water he was maintaining. I would speculate, using a high quality, high protein feed, and having favorable water quality would only enhance the table experience my barber had.