Fixed Gear ratios? (newbie)

I'm new to fixed on a road bike (last rode fixed on a BMX back in 1989!) but have done some SS on a MTB with chain tensioner - 34 front ring or something similar.

I've chosen 42:15, flipped hub I have a 16t freewheel as well. Is this a good 'starter' ratio?

At a cadence of 90 RPM (ideal) it gives me an average speed around 19mph, which is about my aim for training rides. There are two hills on my usual 18 mile (36 combined) training route though. One is only about 100 meters long but has a killer gradient. The other is a 1/2 mile slog with increasing elevation.

I also have another fixed 14t sprocket bought very cheaply (6 pound) from a local bike shop that was closing down.

http://www.machars.net/bikecalc.htm

42T-15 gives you a gear inch of 73.7
87rpm = 19mph,
91rpm = 20mph
100rpm = 22mph

42T-16 gives you a gear inch of 69.1
88rpm = 18mph
92rpm = 19mph
102rpm = 21mph

It depends on the terrain you'll be cycling and how fit you are to push the gears, I run my S/S on 48T 18 which is a gear inch of 70.2, to date I've never have never had to push it up a climb and I've done almost 2000 miles with 90,000 feet of climbing on it. I've only just finished building a fixed gear bike and stuck with 48T 18. It's only been out on a short 10 mile test ride round the town but already I'm thinking the gearing might be too low for fixed gear riding and might drop a 17T or even a 16T on to try.

You can pick up sprockets for a few pounds so worth experimenting with different sizes to find what's suitable for your situation