thermal lift

i am searching for any studies / info on the variation of rising
versus sinking air & specifically the variation of the maximum rate of
rising air within convective thermals.
i am curious how this max lift rate changes with thermal size / total
thermal energy. are larger "spikes" due to smaller isolated and thus
more concentrated thermals?
as a glider pilot (desiring to gain max altitude), for instance, would
one prefer isolated thermal pockets of lift or broader areas of lift
that span more area? or would these offer the same statistical
expected maximum vertical speed rates?
thank you.