Experimenting with stroke rate

This morning I met James, Barry and Kim at the pool and did:

400 - 300 swim, 4 x 25's fast
200 - 4 x 50's kick
1000 - 8 x 125's odd pull, even swim
800 - 8 x 100's odd free strong, even stroke/free by 25.  Less than :15 ri
600 - 4 x 75's IM drill, 4 x 75's fins
100 easy
1500 - 3 x 500's pull with TT desc 1-3 on tempo
1600 - 8 x 200's no equipment with TT desc on tempo

Experimented with different tempos.  Found that a slower tempo felt unnatural, and even took more energy to slow down.  My 'forever stroke' that also was faster than the slower tempo I was able to nail down at around :97-:98 which according to this chart is 61-62 strokes per minute.

What is your ideal tempo?  Not necessarily for a race, but the most comfortable pace that you would consider your sweet spot for a marathon swim? 

Finished up with 100 kick easy

6,300 yards total in 2:00