One thing I will suggest with regard to servos is weight. IMO, we don't need super speed or super torque. But if you want to corner balance your car with the weight as low as possible, it may be worthwhile to consider what kind of weight you want on the left front corner of your car.
I'm not saying it's the most important criteria. Of course not. But it should be a consideration, if you ask me. I run a full size servo and I'm able to get really good weight distribution left/right and front/rear. This was for a TC6 and Xray T4. Can't speak for other chassis...