Better caliper with a bigger disc will make a big difference. Several options, the easiest bolt-ons are Beringer 4 or 6 piston axial with 310mm disc (they make a really nice cast iron one), Motomaster 4 piston with 320mm disc, or the best budget option is the gold Brembo 4 piston and 320mm disc with the adapter bracket that Mr. Peanuts above makes for a very fair price. I've got one and it's nice! You can also change to a radial caliper with a QTMI bracket, although they are not cheap and most radial calipers are pretty wide so you have to watch spoke clearances.
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