like Danno says, read the books.
like he says, 75 miles ain't gonna get you into 'A' shape, California or Tennesse style.
look at it this way, if you;re doin 75 miles, and 30+ of that is on one 'Group' ride, that leaves round 20ish miles for each of 2 other days... not enough. Do at least 25 miles 3x a week, outside of your group ride. Still not much, but at least you'll get to work yourself a little. Even with that, learn to become a tenacious wheel sucker.
Performance Cycling is full of riders who love to suffer. Suffering is the name of the game. If you suffer and can make the others suffer more, itz been a GREAT RIDE! 'A' level riders and racers are mostly sickos!
It gets worse as the age progresses cause the only riders who really stay with it are real sickos! These older psychos even think they have a chance to stay with the 25 yr old sickos, IF they suffer more, ride more training, do more intervals, climb more/longer/steeper hills - really sick...
'A' riders in your area are prolly doing 200+ miles a week, when the weather cooperates. If it doesn't then they're doing only 199+ miles.
Winter/off season - spin your ass off - tempo work - small ring, pick something low-mid 70s, spin your ass off - 95-110 rpm always. the shame of below 95 is never admitted.
winter - you're out on your tempo loop, you come up to another rider slowly grindin in the big ring. You sit 3 yards behind in that small ring and keep spinnin your ass off. The rider drops his head a little, you go round, maybe drop it into that 39x14, and REALLY spin your ass off, you're now crankin at 115 rpm and sufferin. You don;t need no stinkin ipod cause the only thing you can hear is your heart beat pounding in your ears. Rider behind sees you're in the small ring, he tries to come around, you go up to 120, suffer even some more. You're an A rider...