I’ve tried both, comparison:
Best -> Worst:
Comfort: Extreme >> SX (Extreme is very muted)
Power: SX > Extreme
Spin: SX > Extreme
Control: Extreme >> SX
Feel: SX > Extreme
Maneuverability: SX > Extreme
Stability: SX > Extreme
Overall I really liked the SX but the string pattern is really open so it was hard to control, especially on defense. I also had to customize my SX quite a bit because it was very underspec. The feel and connection to the ball on the SX is much better than the Extreme but the Extreme has way better control. Also the SX is pretty stiff so it may give you arm issues but it didn’t bother me.