I have a hitec hs-645mg....would that be suitable enough on a rustler, if not what would do the trick...

More than sufficient. Are you going to be using this for your steering? If so, you can take your stock steering servo (2055) and put that on the throttle link. I personally use the 2075 on the steering and 2055 on the throttle. The 2075 is waterproof and relatively cheap (look on eBay). Only downside is it doesn't have metal gears.

thanks....it's electric...no nitro ...yet...i am waiting to find a deal on one....but thanks for info

Ah ic. Well the 2075 will still be the best bang for your buck. It's going for less than $15 on ebay.