I used to have a 46T which is still 4 bolt shimano compatible. It was a hair faster but it takes more torque and more shifting in response to hills depending on the percent of load that it puts you at. Part of why most non-road bikes went 44 or 42 was because the extra percent of speed was deemed irrelevant under most conditions. A larger difference would be noted by going from 12 or 14(as stated) to 11 on the rear. With a 44t you should be able to get a respectable cruising speed. Personally 80-100 pedaling rpm(cadence) is my fast cruise which gets close to 20 mph. 48T would likely be too high percent of load to sustain in most conditions other than downhill combined with a 11T rear. The descent speed would be handy but how much of your routine would you be able to use it?