It is a matter of taste...Harvesting by Pistil's is not an accurate way to determine maximum potency. If you don't have a scope and have to do it this way...by pistil's, then you look to see if the older pistil's are dying off faster than the new ones are replacing them...At this point harvest.

Now, as far as the correct way. Keep in mind that once a trichome turns amber it is dying/thc deteriorating; So, if you push it too far, You actually lose potency,
so here is where it becomes a matter of taste.
trichomes once they are present only show the potential to produce thc...so, we odn't want to harvest before we get thc, right? oK...Once trichomes start to get cloudy that is the presence of thc...Once the trichomes are almost all cloudy...that is your optimum potency...Now when this happens...some trich's will be amber. some may still be clear. If you go with a higher % of amber trich's before you harvest, you create the 'couchlock effect...lower % of amber and you have an 'UP' high.

Potency also depends on Strain...phenol-sativ/indi ratio...
and of course whether the genetics were any good. Hope this helps. peace

p.s. Before any of you chime in with the 'ol bagseed theory against good genetics...I call Bullshit forward...LOL I thought I just grew OK until I grew some NorhternLights#2
and that 'chit scared me man...later