The gaps from 13 to 15, 15 to 17 and even 17 to 19 are bigger than what I like. On my road bike I mostly used 42x16 for normal cruising. On the heavier hybrid with bigger tires and more upright riding position I find that its 38 would still work well with a 16, but I didn't have one. My area is mostly flat and I used to ride all the time with a straight block 13-19. With the hybrid and my legs that haven't ridden in 2 years I still get by with the center chainring and nothing bigger on the freewheel than a 19. I thought my 13-21 freewheels would be ideal since they added a 14, 16 and 18. Riding with them was much better than with the megadrive even though I got skipping on the 16 if I tried pushing hard. I put on the new chain trying to improve this but made it worse. I put the megadrive back on yesterday for my 40 mile training ride and it went OK although I missed the 14 and 16. I could probably get in the habit of using the 48 chainring but I don't like the chain angle I get with that.

This afternoon I'm going to rummage through my old parts box and find out what other old freewheels I have. I'm certain I have the 13-19 still but I'm not sure what others. I remember a 13-23 that I used to have and maybe a 13-24, but I only have one freewheel remover left and some of those old ones might use a different remover which would eliminate them from candidates for a quick experiment.

And BTW the 13-21 freewheels didn't shift quite as well as the megadrive but they shifted well enough.