Getting ready for .5 conversion

[FullMetalGrave]

Would 9L or more be better? I found a bunch of Feigao's and they are all the same price. The range is 8L motors up to 14L that I can choose from. Also, I would like 3s (for speed/power), but it's not necessary if the 2s pack will perform well. I currently have a 2s 5800mah limn for my stampede that I can test with. I only need it to hit 35-45mph, but the runtime is what I'm after. I would like to try to get 30-45min per pack if at all possible.