Good results doing the 50-80! Yes the 80-90 is what kills you as part of the total time for a 50-90.
Which is why to do a 40-80 instead of a 50-90 if you need that whole 40%. If the 80-90 took an hour, then the 40-50 will take half an hour, so your 40-80 should take half an hour less time than the 50-90.
If you can get by with 30% for a recharge then you save an hour of gen time each recharge. Another excuse to have more battery capacity so your 50-80 is more AH but still in the faster amp acceptance zone--it still takes longer to do more AH of course.
It is all a juggling act.