When you have 12v panels and PWM, the watts don't matter. All that matters is the Isc of each panel, which you add up when in parallel.
All the talk of "lost wattage" using PWM is totally bogus since the watts don't count anyway.
It is also wrong to use the Vmp and Imp of a panel when using PWM--they have no meaning. Just use the Isc.
So the OP can get 16.8 amps as it is now. What he would get with MPPT is a huge variable starting with the battery voltage variable.
With MPPT, amps to the battery would now be OUTPUT POWER (watts) divided by battery voltage. As the battery voltage goes up the amps decline. With PWM you just keep on getting nearly the same amps until near the end of the recharge (see the IV curve for the panel for details)
In practical terms it really is mostly a wash between the two set-ups
