Any 2650kv motor appropriately geared will get you to 70mph, even on 4S. To make it easier on yourself, you could get a lower kv motor and run it on 6S, say a 2200kv, with a bigger pinion. You could get to 90-100mph with the right tires.
For those kinds of speeds you are probably going to need the OFNA foam tires...
http://www.amainhobbies.com/product_...-Dot-17mm-Hard
The biggest problem you are likely to face is that of pinion size. for crazy speeds you will need a large pinion, so I hope the motor mount gives you enough space for a 20-25t pinion, otherwise you may need to find a smaller spur gear.