I am guessing that 30 wins is more rare that 4 x 20 game winners. At least that's true of my experience, but for me it's close. Assuming I haven't missed something, I've had 3 teams with 4 x 20 game winners and 2 teams with a 30 game winner.
I was lucky enough to have one ATG team that combined a 30 game winner with 4 x 20 game winners. The 30 game winner was my #4 pitcher. He may have benefitted by facing weaker pitching opposition. This team won 110 teams but lost the semi-finals in game 7....a heartbreaker!
http://onlinegames.strat-o-matic.com/team/1108035I also had a 70s team with a 30 game winner. This was off of Gaylord Perry's 1972 season, which is 8.46M in ATG8 but is a dominant card in the 70s game.
http://onlinegames.strat-o-matic.com/team/460866I had a 70s team that had 4 x 20. This is tough with the mystery card because often you have to dump one or more of your pitchers since they're in bad years, which means you almost can't win 20 with that slot. This time, I got 4 good years, plus some hitting:
http://onlinegames.strat-o-matic.com/team/401851Then, here's a 4 x 20 ATG team.
http://onlinegames.strat-o-matic.com/team/1112171I may have missed some, but for me--as mentioned-- that adds up to 3 teams with 4 x 20 game winners and 2 team with a 30 game winner, including one team having both.