Master cylinder bore diameter on a dual disc R100R is 15mm, single disc is 13mm, and K1100 is 20mm, with essentially the same callipers fitted between these models. My Airhead in OZ has four piston Brembos over 292mm Suzuki discs with a K11 M/C and the feeling is superb with good initial bite and a progressive feeling. Quality of material in the pads can have a lot to do with it.
*Later K1200RS/GT and K40 series K bikes use a 16mm M/C over dual, four piston callipers. My K100/K1200 Big Block uses a K11 20mm M/C with four piston Brembo R1200GS/GSA/RT-K1300GT/S/R callipers and 320mm x 5mm dual discs, and the bite is stoppie-like with a huge grab but with a controllable feel (EBC HH sintered) - definitely overkill for the bike's weight, but why not!? Stopping is as important as going.
The 2019 thru early '21 BMW R1250GS, GSA & RT were supplied with US made Hayes callipers. BMW had a weep issue with them and for a while last year they were replacing them, if fluid weepage between the calliper halves was evident, with the same brand. As of last Winter there's been a recall and the replacement is Brembo, as it should have been all along. Hayes, or Kelsey-Hayes, is a long-time and reputable manufacturer of brake components, but in this example - perhaps cost cutting or perhaps at a stretch, satisfying the previous administration with US content on imported vehicles - the quality was not there. After the swap and a proper bleed, nearly to a T, the rider will comment that the new brakes (both L & R callipers, new pads, & mounting hardware) seem to have a longer initial lever travel but better bite when braking hard. The cops on their R1250RT-P come back later with a smile after the swap.
As an aside to the recall story the Hayes calliper replacement on the sporty 2019 thru early '21 S1000RR is now Nissin callipers with a new master cylinder, from the previous Hayes combo, along with a software update.