I believe (but am not certain) that two 36v strings in parallel will halve the amps that each string sees, so yes, it might reduce Peukert's and extend range. (In series, I think each battery sees full amps.) On the other hand, at 36v, you need more amps to do the same work.
In a loud announcer voice "You are correct sir!" ding ding ding.
Personally I would lean towards 48v bank at this point, like you noted it's less batteries overall and less load per battery for the same "speed" and more potential top end power but not for as long as 2 strings of 36.
MetroMPG: I am following your project and progress with great interest. Thanks for keeping us posted. You could consider your recovery and recycling of the dead batteries as purchasing some more green energy credits.
On the junction, you can use a acetylene torch to heat up the nut and the junction, so that you can get it loose. Pretty freaky thing when the brake lines are rusted enough their breaking open, but you can't get the stinkin fittings loose. Best of Luck.