I am sure it would be fine. IIRC, the calipers have 4x32mm pistons, so the said master, set at 21mm fulcrum (creating a 16x21 master), would work quite well. I am running a Galespeed 17x17 (17.5mm piston and 17mm fulcrum length) radial master along with a pair of calipers with the same piston configuration (Nissin monoblocks from a 2010 Daytona 675) as the the GSX-S's Brembos and the combination is sublime (bike is a heavily modded 1999 VTR1000). The lever is soft, feedback is awesome and power is incredible; I suspect you would get a very similar result here. Some will try to steer you to the RCS19, but IMHO, even at its shortest fulcrum, it's still too firm (from one who likes a relatively soft lever for the added feedback it provides and improved modulation if offers). Far too many mistake a firm lever for braking power, don' fall into the trap.
FWIW, over the course of many years of experimenting with many varied and various braking components, I made the jump at one time from the Nissin 19x18 (which I believe is what the GSX has) to an OEM Ducati Brembo (the 18x19 unit used on many/most late-models ducs with M4 calipers) and the improvement was noticeable. May be another (cheaper) option for you.
Last edited by mikstr; 07-30-2018 at 10:09 PM.