The options can be many and varied, 4 pot Brembos will fit but need an adaptor bracket as the caliper mounting holes are wrong. Mk1 caliper mounting holes are 90mm apart. This spacing was common to plenty of other bikes such as Kawasaki ZX7R, ZRX11/1200, ZX9R, ZX6R Suzuki GSX1400, Hayabusa, GSXR1000K1 etc
The standard 4 pot Nissin calipers IF and I repeat IF in good order perform brilliantly, enough power and feel to get the job done. The only reason they feel lack luster will be down to maintenance ie: lack of power or too much lever travel.
A factory option if your pockets were deep was to go for some Alcon 6 pot calipers, these are billet aluminum rather than cast items and have Teflon coated pistons which aid performance and longevity. Alcons in my opinion may have more ultimate stopping power than the stock 4 pots and their performance doesn’t go off as quickly as the stock brakes so lever travel is always maintained.
They do however have less “feel” than a well set up set of 4 pots so as with most things there is a trade off. But hell they look trick and are generally sought after
Aftermarket items such as Billet 6 pots, Beringer and Nissin 6 pots all do an option to fit too
Speaking of 6 pots a pair that split opinion are the Tokico, these can give poor performance if unmaintained. I have found when rebuilt with red rubber grease on the seals they perform ok and I used them for many thousands of miles on my year round bike in some terrible conditions !
The only thing I did when fitting my calipers was to go to a twin line set up. Thus loosing the central hose splitter, replacing it with a couple of P clips
A couple of cosmetic mods on the rear caliper for me included replacing the brake torque arm and drilling the caliper hanger.
The brake torque arm from a Honda VF1000R fits, all that is required is to press out the bush on the end and replace with the one off your torque arm. I like the perforated look of it.
Drilled rear caliper hanger