There's no doubt that the brakes on the S2R 800 can feel a bit lacklustre compared with some of the sportier models. There are a couple of reasons for this:
First, the discs are only Ø300mm compared with the 320mm of the other models you mentioned so you're getting considerably less braking force than with the larger discs.
Second, (if I remember correctly), the standard calipers are only two-piston sliding units, rather than the four-piston opposed types of, say, the S2R 1000, so, again, there's less braking forces acting on the discs.
Some points to note if you're planning an upgrade, because of the smaller discs, the standard calipers mount on an adapter plate, whereas, with 320mm discs, the calipers bolt direct to the fork legs. See following pics...
Upgraded calipers come with either 40mm or 65mm between the mounting holes. I'm not sure either will fit on the adapter plates with the standard discs, although, if you're upgrading the calipers, it would be a false economy not to fit the larger discs at the same time.
I fitted the 65mm, four-piston, four-pad P4 34 Goldline calipers to my S2R 1000 together with Galfer discs. When I sold my bike, I took off the upgrades and sold them to a friend with an S2R 800. The 320mm discs and Goldline calipers bolted straight on and worked perfectly with the standard coffin master cylinder. Interestingly, Ducati used to offer a DP disc and caliper upgrade (320mm discs with P30/34 two-pad calipers) and that used the standard master cylinder, so I don't think you'll need to change that unless you particularly want to.
If you want to go down the single-disc route, there's information here about suitable master cylinders
http://www.ukmonster.co.uk/monster/s...d.php?p=556431 Brembo recommend a 15mm RCS master for single-disc four-piston setups.
Of course, if you do upgrade the brakes, that'll probably show up how bad the unadjustable forks are and you'll then want to upgrade those too! It never ends!! ££
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