Daniel, I flew my Mountain Models tantrum with the same motor and gear as you. I found that a 2S 1500 Kokam and either a 12x6 or 11x4.7 an ability to hover at around 60 - 70%throttle!!!! I have not tried a 3S on the 350.

I have also found that my tantrum kept the motor relatively cool with the 11x4.7 and just slightly warm with a 12x6!

I have since switched to a Himax 2015-5400 on the same gear and WOW!!!!!!!!!!!!!!!!!!!!!!!!!!!!! 2S will hover with the 12x6 at 1/2 throttle, and only draw around 12 amps at full static!!! 3S and a 10x4.7 ... SSSSWWWWWEEEEEEEEEEEEEEEEEETTTTTNNNNEEESSSSS!!!!

I think the 2S will give you good performance, the 3S will obviously be better. BUT the 3S will wear the motor out a little faster.

Just my thoughts,

Reg

PS My last 350 with D has about 2 hours of run time on it with a 2S and 12x6 and would still be running strong!