I run 41psi and have no issues. Here's an idea:
You said its your rear tire under braking. Perhaps the front is so sticky your using it extra hard and your loosing weight on the rear, hence the lockups. Use your fronts hard enough and the rear is completely useless for braking anyways. I suggest you stop using the rear brake completely and learn to brake correctly.
'06 F4i: racetech front springs+valves, ohlins rear shock, steel brake lines, 'mura slipon, 88K miles
'08 600RR- steel brake lines, shorty brake lever. Stripped track bike.
'15 1000RR- Flapper mod, 08-11 gauge swap, hotbodies fender eliminator