I remember my parents Hoover Electron 800, brought back in 1986. Despite it's top speed being 800rpm (considered slow these days), clothes seemed to feel dryer than many 1000 spin machines I've owned over the years.
My own first automatic was a Servis Easiwash 600, back in 1992. I would spin for 5 minutes at just 600rpm, and though not great, you couldn't physically ring out any more water from heavy items such as jeans and towels.
For a number of years, I ran a hotel laundry. We had two Primus 10KG automatic machines, with a max spin speed of 400rpm. Towels would be put in a 5kg hydro-extractor once taken from the machine, and spun for 5 mins at 1450rpm. This seemed to be the most efficient amount of time. The amount of water extracted from the load over 5 mins, was negligible, being just a trickle out of the waste pipe at most.
My washing machine (an AEG 76669) has top spin speed of 1600rpm. The cottons spin dry lasts 9 minutes or so, with the last 5 mins or so at the top selected speed.
I only ever spin at 1200rpm as this seems to remove enough water . I have noticed the fuller the load, the dryer the clothes seem to feel after the spin, possibly because of the drum being well balanced? In summer months, when I'm able to peg clothes on the line, I tend to spin at just 900rpm (my machine has variable spins of 400rpm; 700rpm; 900rpm; 1200rpm; 1600rpm), which saves on ironing.
Morgan