would agree,You have said 3 things there that if you put 60 PCs on 2 circuits with RCD protection, you would not keep the RCD from tripping as I think you have forgotten or you didn't know that the PSU on the PC has leakage due to the filter circuit in the PSU. Therefore you should be looking at 10 PCs per circuit as you may have approx 2.5mA leakage per PC by the time you take the base unit and monitor into account.
except 8 per circuit, allows for some leakage/error.
whether RCD protected or not I would still do 8 points per circuit, helps with the segregation too, just a lot more circuits,
tho Im not so sure about being totally able to do away with RCDs in a school enviroment where kids are using electrical equipment.