I am not familiar with the chemistry or the CDR of those Aspire cells, and to honest if Mooch hasn't tested them I wouldn't use them.
I would recommend investing in another two cells of known and tested CDR like the Samsung 25R or the LG HG2.
Ryedan's advice is right on the money about calculating the safe amp draw based on the minimum charge divided by the number of cells. However the iStick 100 uses a parallel battery config with buck/boost up to 10 volts.
So at 3.2 volts when the batteries are ready to swapped out, the amp draw is 17 amps per cell which is below the 20 amp CDR.
You can see the maths behind those calculations
here, and/or use
steam-engine to model them.
Remember with a regulated mod