I have an Evoluzione slave cyl which, I believe is 28.5mm and it really needs the 4-way lever setting on #1 (largest span) otherwise neutral can be tricky to find, especially if the clutch pack is slightly thicker.
Although I have since removed 2 springs from the clutch and with the right clutch pack thickness could probably get away with #2 setting but I like #1 as it suits my hand size.
If you go too large with the bore of the slave cyl you can get clutch engagement/disengagement problems which also depends on which master cylinder ratio you have.
Shazzam posted a useful chart showing the effects of different cylinder/ratios that may be of help;
FWIW, after four years of use, approx., 15,000 miles, my STM slave cylinder started to leak. I'm not sure whether to judge this a reasonable expectation of life... maybe. I've put on an Oberon slave cylinder now.