CSG, your question is subjective ('what is good for me'). Here is an approach that will help you to figure this out

1. Compute the gear inch of the gears of your MB (search for sheldon gear calculator)

2. Get the gear inch of the Brompton configuration(s) you are considering (this has the GI range http://clients.squareeye.net/uploads...nt_20x20_2.pdf notice also the reduce/raised gearing options, interpolate the middle gear or get from people that know). Don't know what is your mathematical background, if you have questions feel free to ask.

3. Match the brompton gears to gears on your MB (use closes gear inch value)

4. Ride your MB using only the matching Brompton gears and see what you like.

BTW, I am using 6s reduced gearing and using all the gears.