Hello Ben! I hope you survived the super storm with little damage for you and your family!
MTS has been well received for performance.
Storm SL is a lighter rotor with more aggressive cut-outs which have a great initial bite but also wear pads more aggressively.
The Storm rotor will take more heat and endure more abuse.
Yes, new brake compound since 6 months now and much stronger feel with them.
The "S" uses a "MT4" carbon MC body but with a lighter folded alloy lever blade as apposed to cast alloy blade combined with the nicer, lighter and more rigid one piece caliper body with adjustable pivoting banjo fitting. (MT4 and MT6 calipers are the same aside from 4-paint/6 anodize)