I did a minutes slow warm up and then 20 seconds max effort, with 10 seconds rest x 8 and hit just over 1300.

I came pritty close to breaking the 41minute barrier for a 10KM with a few stops for water in the summer.

Be interesting to see what my 4 minute time would be though going to be a while before I can find out.

For the record I was under the impression the 'difficulty level' people often refer to from 1-10, doesn't affect resistance at all. It affects the catch position which is when resistance is introduced on the stroke. 10 being right at the beginning and 1 much further back. Supposed to simulate different weight boats/people in regards to boyancy.

I may however be completely wrong and speaking out of my poop hole