Spartacus
yes, it is hard to compare 20 reps and 1 rep, unless one trains for both.
i have always got about 20 reps on 70% of my max, although probably would not if had strict lockout on each rep.
when at peak and benching about 170kg (without pause), I could outrep my mate on reps, although he was a lot stronger for a single 9about 200kg). Fact was i have always done a lot of reps (and short rests), whereas he was always doing sets of no more than 6 reps (with full rest).
I read in one Soviet sports Review in 1980s that 1 rep means 4 reps on 90%, 10 reps on 80%, and 20 reps on 70%.
While it works out roughly for me, many other books have different interpretations.
As PTC indicates, depends very much on training specificity.