In article , Martin Brown
writes

Depending on what they are 1cm round the edge would probably be OK for 4" pots.
They are most easily repotted early in the year unless extremely pot bound.
Overpotting tends to cause rot via wet roots. A hint that it needs repotting is
when roots start coming out the bottom of the pot.

You are sensitive to your plants needs! ;-)
For me, the hints are
1) the pot starts falling over because of the semispherical bundle of
roots through the bottom
2) square pots begin to look circular and circular pots begin to look
square.

I suspect your way is better for the cacti!
--
Kay Easton

Edward's earthworm page:
http://www.scarboro.demon.co.uk/edward/index.htm