I have been trying out bikes at various stores, and don't always like the gearing.
All have 48/38/28 teeth in front, but in the rear they have 11-32 or 13-34 or something
else. It feels that 48 front/13 rear is too low for top gear, but maybe that's a false
impression -- I have not been able to test-ride anything down a big hill. My current
crappy bike has 51/14=3.64 as top gear, which is too low. I tried a comfortable bike
yesterday, but its top gear was 48/13 = 3.69, which also felt low.

Questions:
(a) Am I naive too think there's much difference between 48/13 and 48/11 in practice?
(b) How easy is is to replace a rear 13-32 cassette with an 11-32? Do I need to replace
the chain and the derailleur?