30 rounds is not "realistic" in my book, considering the inaccuracy and lack of range of airsoft rifles.
Jeff, I use TM Standards and have done so since I started airsoft. No jams, no problems at all. I beat the piss out of them too, and they take it! I have 11 mags (for a 10+1 loadout), and have never needed more than that. I usually carry 8+1. Like you said, you've never even needed that many rounds in a real firefight. Keep in mind though, airsoft range an accuracy leave something to be desired!
I have also used a CA HiCap in my M4 without a problem.
Same with STAR 30-rounders. I had no problem with the ammount of BBs in each mag, but prefer 68 rounds to overcome the inconsistencies of the gun.
That's all I've used. Any opinion about mags other than that would be "what I've heard", and I don't get down like that!