Another Batt/ Motor/ Esc combo question

[lambchops]

I know its allways asked but I want to be sure im buying the right combo.

My and my dad both run Hyper9 Nitros and I also have the mbx5 brushless with MMM3, 2000 kv medusa and 3x 4380 25c 4 cell flightpower lipo's. Now dad is allways having Nitro engine trouble so he's decided to go brushless with the hyper as thanks to marvin have just found out all the diff parts are the same so can use the 9e mount as a direct fitment.

So my quesiton is what motor and Batt should I get for him, I have the Monster Mamba which I love and know so think I will get him the same Esc but what about motor... what about 2000kv tekin or is that to much? Would like to keep it on 4 cell bats as then we can swap/ changes batterys, would also like 20 mins run time so he can complete a nitro final! Was thinking of the 5500 25c Hyperion, my 4380 flightpowers do 15 mins so think this will be enough...

Any sugestions?