I dont know if PS3 use RPM to check fan speeds but it only sends DPM message how many volts of power that fan will use to speed up its fan. And these DPM sent to fan is based on temperature that read by PS3 thermal sensor on CPU.

0x60 is nowhere 50% of fanspeed

the range is from 00-FF (safe speed is 0x50 anything lower than that may cause overheating)

0x60 is probably somewhere 30%
0x85- 50% fan speed

the only thing that sony limits the fan speed is to decrease to annoyance of players for their noisy PS3.