New to brushless, what pinion should I use?

[Krawlin]

Well, to start out, would like to say hi to everyone, and I am new here!

Well, anyway, I have a 3906 E-Maxx thats been upgraded (not nearly as nice as most of the Maxx's on here, but its gets the job done). And over the past 10 months, it has stayed brushed, and I am ready to go brushless and Li-Po. (You guys can blame Takedown and Brushlessboy16 for this... )

Anyway, so I already picked the motor that seems to be just right for the job......

A Medusa V2 Afterburner 36-60 2000Kv motor.

I already have a Mamba Max ESC, and I plan on running two 2S Pro-Tek 4000 mAh 30C Li-Po packs wired in series for 4S.


Now my main question is, what pinion size do I use? Remember, this is the 3906 E-Maxx with a 2 speed tranny, (just go by running in 2nd gear all the time), the diff gears are stock, and it has a 66 tooth spur gear.
Now with that in mind, I am shooting for the 40 to 45 MPH range on 12 cells Ni-MH and 4S (just go by running on LiPo most of the time).

So, what pinion should I use? Someone told me 19 to 21 tooth would be perfectly fine, while someone else told me I should run something in the 23 to 25 tooth range. So what pinion should I run?

I know zero about this brushless stuff so I am pretty much lost.....

So is the Medusa V2 Afterburner 36-60 2000Kv motor a good choice? If not, what would you recommend? I am on a bit of a budget here.

And what pinion size should I use for the motor I chose, or if you recommend a better motor, what pinion should I use for that? Remember I am shooting for at least 35 MPH when running 12 cells Ni-MH and 40 to 45 MPH on 4S Li-Po.

(and I am on a bit of a budget, my GF won't let me spend too much on this.... )