recursive-clients recommended values

[blrmaani]

Sorry for the repeat post.. but I know that the value of 'recursive-clients' option is based on:
1. Query rate
2. RAM size 

and various other factors. I vaguely recollect that it is 
90 x <query-rate> x <something> , but I forgot why...

I searched earlier posts but noticed that people are recommending it to just increase it to suppress the errors in log.

Any pointers on this?

thanks
blr