Well after a darn good thrashing around Mallory Park (I'll get some pics of the event in the gallery soon) I am none the wiser... The good news is that the bike did not miss a beat. BUT, at no point in the circuit did I manage to get into top. 3rd gear at best! I can now see why the RRT2 box was such a good idea for circuits. One thing I did do just before I went out, was to change the plug cap. I had done so before, but something told me to swap it again - so it's got a nice NGK cap now. Either this has fixed it, or it really is just a 4th gear issue. Could also be the fact that I don't recall dropping below 4000 rpm very often (apart from the hairpin). So maybe I was just avoiding the resonant frequency that was causing the fuel to froth? I'll try it again on the roads over the next couple of days and see if anything has changed. If not, then I'll just have to keep it for track days!
N.