how much current is enough?

I know that to gain 3db of additional headroom from your speakers you need to double the power from your amp...given that, its easy enough to calculate how many watts will be suficient to reach your speakers rated max volume level before compression...or to see if your amp will play loud enough for your particular listening habits...
and i know know that watt/sq.rt of resistance = current ...so i can calculate how many amps my amplifier will put out into various loads, but i dont know how many amps are enough for a given speaker...or if the difference between say 10 amps and 12 amps is a lot?

with regards to a specific difficult to drive speaker the Totem Mani 2 how much current is enough??

its specs are
4 ohm nominal...it drops down to 2 ohms, all resistive
81 db sensitivity at 1w/1m

and it uses an isobaric configuration which i gather makes it require more current than normal..but again i dont know why or how to calculate it...

so from a mathematical point of view how do i figure this out...

and in terms of the ability of am amp to put out lots of current what specs are the most important to look at?

thanks