Good base for a E-Revo build

[miniGranis]

What about motor choice. I am abit concerned about heat, since I wont be using more volts then 4S and 8000 mAh, would the 8XL heat up too much ?
Would the 9XL be a better choice as it, if I got it right, would run cooler ?
I really want to use the full capacity of the batteries without having to worry about heat. Also I wonder how much slower and 9XL would be compared with an 8XL. (I tried the magic RC calculator but there are too many unknow variables to me).
I know pinions and spur, tranny gearing etc would have an impact but if possible I would happy for any "general" comments regarding the 8 versus 9 choice.
I have a Hv-Maxx (6.5) today and a bit more speed out of the Revo would be nice, also the Hv-Maxx do suffer from heating issues (but thats pretty normal to the Hv-Maxx).