1. I don't remember. My buddy was running 4S on his Flux for awhile and I know it would wheelie on command. However, until he went to 6S I don't recall trying any standing backflips. Probably depends on tires and how much traction you are getting.
2. Depends; what is your overall gear ratio with the Savage SS? What size tires are you running? Flux has some pretty tall ones (6.3" diameter) but it should run around 40mph OOB on 4S (according to the
Script Asylum computations).
Total gear reduction for a Flux is 14.65491, for a Flux with the bullet proof diffs its 14.27623. Flux gearbox is 44/18 x 29/32 which is the same as a Savage X's 1st gear (2-speed gearbox).
Also what is the Punch set too on the MMM? Maybe its too low, you could try setting it higher and see if that gives more instant power to the engine.
4. Yes. Theoretically (again script asylum) says that'll be ~64mph. Probably want to run with less than 100% punch. Also probably should monitor temps more frequently.