I have 5 cell batteries (actually a bit more than 6v) in my DP Extra....

As for whether to use 5 cells or not, it depends more on the radio equipment, rather than the plane, in my opinion....

I use hitec digitals, as well as hitec 645's, and 6v works fine...I also use two packs, with dual switches....

Whatever floats yer boat....er....flys yer plane....!