20grit - while a 39T might suffice, don't be mistaken about inclines in SoCal! My riding enthusiasm is fueled by climbs. The longer the better. When I visit my wife's family in LA, I hop on the bike right from their house and do some really steep, long roads. Continuous stretches of 4-6000' vertical is not uncommon in LA's San Gabriel mountains.

For me 39 front-28 rear will do most things except the oddball 15-20% hump some guys were writing about earlier. As my knees age I'm starting to see the compact advantage, though. Either the 39 ring or the switch to a compact crank/new BB is not too costly. Long cage classic Suntour derailleurs are still affordable on eBay.

Good luck!