I'm using a 48x34 chainrings with 11x25 rear cogs. I live in san francisco and my house is at an elevation of about 800 feet above sea level. For years I have made do with a 53x39 and 12x25, but the compact cranks allows me to spin faster up the hills and the shifting has been great. I could not find a 11x25 cog set but I took a 11x23 and put it together with my 12x25. I spin out with a 48x12, but the 48x11 has been great! It's almost the same as a 52x12 and I'm able to pedal at 44 mph. FSA sells a 50x34, the 50 produces a 112.5 gear inches, 48x11 produces a 117.8 gear inches, 53x12 produces 119.25 gear inches.
The advantage to the lower gearing is that I'm able to stay in the big chainring on most of the flats and rolling hills.
I'm going to have one bike with a compact set up for the hills, one standard double with 27 cog in the rear, and a commuter bike also with a 53x27.