A Savage is a beast of a truck. I tried running my 1515 2.5d on 6S and it does get warm, depending on the gearing and that is in a truggy.

For the heavier Savage, I'd try the 1521. Besides, I don't think that a motor being able to spool up quickly will matter with a Savage. If you do go with the 1515, I'd go with the 1500kv motor for 6S