Juice panels are either nominally 12v or 24v depending on the size. If the maximum "open circuit" output of your panels is around 36-40v then they are actually nominally 24v panels - the same voltage as the larger Juice panels.
If you need smaller panels then two 12v panels can put in series to make the output nominally 24v (actually maximum around 36-40v open circuit).
It is true that a higher voltage set up will give better low light performance because the panels will only charge when their output voltage is higher than the battery voltage. Even an MPPT controller will only charge