Starting with rated Watts - say 4 125W panels, 17.3V, 7.23A wired in series...

If everything was perfectly efficient and real life equaled rated life...

Using an MPPT controller I should get Vmodule/Vbattery*Imodule amps into my 12-volt battery bank.  69.2V/13.5V*7.23A = 37A.  I used 13.5V as sort of an average between 12 and 14.7.

Now, I've got to factor in the inefficiences:

Real life panel Wattage - 80% of rated
Controller efficiency - 93%

So my 37A becomes 37*.8*.93 = 27.5A.  

That's about 20% higher than I'd get if the four panels were in parallel, assuming the same 80% "real life" reduction, so that jives with some of the earlier comments.    

Are those reasonable percentages, and are there other inefficiencies I haven't considered?