Pamestique 

Hey Welcome to BF So Cal Thread. Don't limit yourself here and also post on the road riding forum.

As to bikes and sizing... there is no set rule. Just know you may be a 54cm on one bike but a 56 or 52 on another. Bikes all have different geometry and measurements. For instance I am 5'8" and have 3 road bikes - a Lemond, a Leader and a custom. All sizes are different (51 cm, 54 cm and 52.5cm).

I don't know the bikes you are looking at. I can recommend some other shops to try such as RocknRoad in Irvine (off Sand Canyon and Irvine Blvd) and Surf City Cycles in HB. Also try Orange Cyclery near the Orange Circle. Bottom line, get a bike that fits and has fairly decent components. I would try not to go below Shimano Sora or better would be 105 or ultegra.

Once you get the bike... look up the Bicycle Club of Irvine [bikeirvine.org]. The first Saturday of each month they stage an intro to cycling/club ride.

Good luck and have fun shopping.

Edited to add: Most top end bikes now come with Shimano 10 - which means 30 speeds. My older bike is a 9 speed (27). If the bikes you are looking at have only 24 speeds, then it's low end componentry which you won't be able to upgrade. I would do alittle research about bikes and components before you buy.