those are solid numbers just watch for temps. as 64 is close to a safe max.
do you have fans set to 65%?
the newer batch has 1 fan so I would play with fan number's
see what 55% = in rpm
see what 60% = in rpm
see what 65% = in rpm
go up to 80% as I think 80% is the max fan speed not 100% (I don't have a 1 fan s-7 so I am not sure.)
BTW I spent time in the USN 5 years 1978 to 1983
i have 3 s7 with 1 fan, my fan speed all set to max 100% = 5880 rpm, no choice the temp. here now is 35'C.
then tell us rpm please at 90%
if rpm does drop to 5500 at 90% check the temps very carefully.
basically fans at max rpm and fans at just under max rpm cool the same.
ie a fan running at 5500 rpm should do the same as a fan at 5880 rpm.
and that slight underclock makes fan last a lot longer.
It is a sweet spot all fans have it and it depends on the fan and the heat sink pattern.
If you can run the fan at 5500 rpm vs 5880 rpm and not overheat you will save some money.