Very good tips. Testing the traction level with the rear brake is the best you can do. Of course, modern touring tires like the Pilot Road 3 or the new Z8 M/O do help a lot. Most important is to be smooth, whatever you do, do it smooth. Smooth throttle, smooth brakes, smooth turn in and you can do a lot in the rain.
In general I do slow down a bit in the rain and am less agressive on the throttle (I have ABS, so braking isn't an issue) so I end up vaguely at the posted speed limit. Through the courners I do add a little bit extra cautiousness.
If you stay relaxed and don't push it, there's no problem with riding in the rain, take a look:
Into the dark side of our nature to look we all need. The energy, the passion there is. Afraid of that people are. Pieces of us it holds busy denying we are.
Riding is flowing through traffic like water through a rocky river bed.