If your hams are very strong - then a high saddle position is better. The hams are used on the "upstroke" (i.e. when pulling up at the back), and a more upright position allows a stronger pulling motion.

The quads are used when mashing down - which is the strongest motion for most cyclists. A lower saddle position allows a stronger downstroke, so your LBS probably wanted to put you in the 30-degree position assuming that you would mash down, as most riders do.

I'm surprised that your quads aren't your strongest muscles - all that time in the gym must have included plenty of squats, which build quads and glutes.