IT'S NOT THE CALIPERS
Sorry to shout but this is always the first thing people look at, whilst they overlook the brake fluid pump attached to the lever they actually pull to activate the brakes.
Change the master cylinder...Night and day difference on any Japanese bike, and cheaper than callipers.
Recommended order of upgrading brakes.
Fluid (use good quality Motul RBF 660 or other Dot 5.1)
Pads (Use decent sintered pads like SBS, Brembo)...If dry track only...Try carbon brake pads...You need to bed them in.
Braided brake lines (Goodridge, HEL they're basically all the same).
After all that, do the master cylinder...Accossata...Brembo...AP Racing...Unless you are a top level racer they're all the same and all better than stock.
Next discs...Personally I would just use Brembo.
Lastly callipers...Again Brembo or AP Racing...But this is serious performance level that I'd argue most don't need.