...oh, by the way, tried DOT5, didn't improve it much. DO have some cast iron rotors, might try them next. This is probably me being pedantic, my Super Blackbird stops on a dime, but I'd like the same braking on my ST aswell.
Just a couple observations (I ride an ST1300, so no direct experience with the ST1100, but I suspect general performance with proper OEM components is similar. Other owners of both - feel free to opine...):
Bear in mind the relative weights of the bikes. Super Blackbird dry - 494#, ST1100 dry - 633#. This is a HUGE difference. Kinetic energy is kinetic energy. Assuming equivalent tires, weight transfer, etc., i.e. only the bike weight being substantially different, the heavier bike will take longer to stop at threshold braking (verge of tire skid) than a lighter one, in somewhat linear proportion to weight difference. KE = mV?/2, m being bike mass or weight. The ST will always have a longer stopping distance/lower deceleration rates (by some 20+%) from a given speed than the Blackbird. You could put the most monstrous, bad@$$ front brake system on, and it just means you could lock the tires with lighter input pressure. ST will never stop as fast as Blackbird - laws of physics. Your rate of energy dissipation is limited by your frictional force between tire and road surface. Grippier tires could help a little, but only if you are riding in that 90+% performance envelope - approaching track racing limits.
It sounds like you couldn't lock/skid the front tire even if you wanted to. Can you skid the rear with moderate pedal pressure? I am certain something is wrong in your brake system due to pad wear at minimum. I cannot hazard a guess as to what it may be, but it seems focused on the front system (large percentage of stopping power).
One caution - many brake system soft components are damaged by DOT5 Silicone brake fluid. It is incompatible with non-silicone fluid. System must be throughly flushed out, hard parts cleaned with solvent, and thoroughly dried, and all rubber parts exchanged (seals, hoses, etc.), before any switch of fluid type (if all soft components are switched to DOT5 compatible materials). If you switched back and forth between DOT4 and DOT5 without this flush/clean/replace, and/or continue to use OEM soft parts with DOT5 fluid, some of your MC, hose, or caliper internals may be damaged.
Are the MCs OEM and in good condition? Same Q for calipers and rotors. Has the system been properly bled of air? Is the lever collapsing all the way to the grip before threshold braking levels are reached? Same Q for rear pedal. Are you trying to directly compare stopping distances/deceleration of the ST1100 with the performance of a lighter (much lighter?) sport bike (as described above)?
The brake pad wear defies belief at fully gone in <4k (km or miles). For even aggressive street riding with the grippiest, fastest wearing pads, I can't believe this pad life is reasonable. My ST1300 has 25k miles on it, and I just checked the pads and they are barely over 50% worn. I don't "track ride" on the street, don't do any high speed stopping on the street, but have had it on a racetrack before. Just a possibly meaningless comparison FWIW.
My opinion - Feel free to throw a bunch of money at the bike with a bunch of aftermarket parts, but I think your efforts along those lines
are likely misdirected.
YMMV. Hope this is informative.