I had an ST4S which I ran on both BT010 and BT020, and also for a while BT020 on rear with BT010 on front (Bridgestone recommended, put the stickier tyre on the front). I also had a 180 rear instead of the 190 it came with. It handled very well, and seemed to turn in quicker, but I was not very experienced at the time so might be imagining it.
I reckon the Bridgestone "dual rubber" tyres are really good, and I got good mieage out of the BT020 - about 5k miles. Running on Pirelli now on the 749S, and get about 2k miles out of a rear. Go figure.
[Edited on 31-8-2005 by HW]