Maximum Action Points = cap for a given turn for which you have points saved.
Calculated using Constitution+Base.
Start Action Points = the # you start a battle with.
Calculated by (Speed*0.5)+(Perc*0.5)+Base rounded down to the nearest whole number.
For instance I have 11 Speed and 10 Perc and a Base of 2. Therefore I have 12 total starting AP
Turn Action Points = number you gain in turns after your initial turn.
Calculated by (Speed*0.5)+base
I believe this is the number displayed on the character sheet as AP.
Summary
Constitution affects max potential AP on a given turn.
Perc affects AP you'll start a given battle with.
Speed affects starting and regular turn AP.
Glass Cannon multiplies the AP regen by 2, so speed is not a waste.
Just make sure that your Max potential AP is as high as your AP regen by increasing constitution as well.
http://www.larian.com/forums/ubbthreads.php?ubb=showflat&Number=509068#Post509068
