I bought my largest Angel back in October, at in-between nickel and quarter size, and put it in my 29g along with 3 SDs, a Pim. Mysteriosus (recently learned, i was thinking blochii), small BGK, and a Striped Peacock Eel... Needless to say the tank was at it's bioload max, but still had fairly decent water quality. The nitrates weren't exactly good, but weekly water changes of 25-40% helped a bit.
I fed him freeze dried bloodworms, tetracolor/min tropical flakes, wardley's shrimp pellets, and earthworm/nightcrawler pieces - all in small amounts 3-5 times a day. He is now an easy 5" TL, if not more, and in amazing health.
Water quality is a big factor, but obviously other things play bigger roles, mainly a healthy, varied diet. I kept the tank at 78-82 degrees.
Personally, I would not raise the temp any more. It's not needed IMO.
The eel, and knifefish are in a different tank now, FTR... lol