Hi Tim,
I’ve run then both BA & Cobra 2826 and they are great, they like the 5 cell batteries and perform very well with lots of power and reserve left in the battery. I’ve also have the BA 3515 installed in a new model but haven’t flown it much yet (snow is too deep yet lol).
However biased on others I think it will be a good choice as well, however, it is larger electric motor, so far it works great on either 5 or 6 cell packs. I understand you are limited on space in your model without a total rebuilding the front end. I would be install the BA 2826 and go flying and have fun. You might want to consider building a new model for the 3515-710 motor.
Later,
Mikey