[Bill]

There is not so much difference that you will go from 'nothing in my feet' to 'too stiff'. In your case, I think the only time that the 30s may feel better is on the surface. Testing on a dive will tell you more. Yesterday I timed a 30 meter dive with my old 30s to compare with the Mustang 40s that I've been using. It took a little longer to get off the surface and the kick was a little faster. The dive was 4-5 seconds longer but felt easier. When my legs are stronger, I'll try the 40s again.