I too had an FZ-09 prior to my GSXS. The FZ had some of the same inherent problems out of the box .. snatchy throttle, way too much engine braking and poor suspension. I flashed the ECU and ran full aftermarket exhaust on both bikes to correct the engine woes, and also did suspension upgrades.
The Suzuki is more refined, better build quality. I would say the FZ is more fun to drive around town and do easy wheelies, and the cross-plane 3 cylinder motor has a great sound and lots of torque. Flat out the GSXS will scare the sht out of you once you hit 7,000 rpm to redline, the in-line 4 cylinder K5 based motor is a beast! Will blow the doors off the FZ in a drag race.
I like the gear ratios better on the FZ, the GSXS's are too close. I would say trying to put it into perspective, the FZ is more a fun hooligan toy, the GSXS a more solid, refined serious bad boy.
I swapped bikes with the friend that bought the FZ from me on a recent ride, and the FZ felt smaller and much slower. I couldn't wait to get my GSXS back. I do feel the GSXS was a definite upgrade from the FZ-09.
You would love either, I think it comes down to which one you are more drawn to personally.
Last edited by Rapido1; 07-05-2019 at 08:39 PM.