Monster angelfish!

I went to my LFS yesterday and saw this huge angelfish (from a guy that was tearing down his tank. I felt bad because it looked like it was gonna die. It was flipping around and stuff =/). Body size was maybe 3 inches or more. It seemed as if his body would cover most of my palm. I've had people tell me my angels will get that large but I honestly didn't believe it at all until I saw this guy. I was wondering, while I know fish growth relies on many factors, given a best case scenario will my angels get this large? They don't seem to be growing fast at all and they get quite a bit of (what I think is high quality) food and the water temp is 80 if that matters. Here's some pics of the big guy







So I just thought it was really cool because this guy is huge but also wondered why my angels almost feel like they're not growing much. Do they just grow slowly no matter what? I've had them for about 2-3 months depending on which one.

I feed a frozen food called cichlid delight and a small pellet called cichlid xtreme I believe. Water changes 20-30% every week. I just also read a stocking guide by JM. He said angels can get to 6 inches across and 10 inches tall with fins. That was awesome to hear. I like the idea of my angels getting huge.

Yeah, I actually did about 20% or a little over every 2-3 days until fairly recently (a few weeks or so). I mean these angels aren't small by any means. Their body's are anywhere from an inch and a half to 2 inches (just the round meaty body, top to bottom). I honestly don't know how young they are (however old they were at the LFS plus 9-12 weeks). Do you think at that size I should still consider it a grow out tank? I have no problems doing that.