Well, for my single spark model I'd recommend the Splitfire triple platinum (part number TP392C) I was amazed at the difference they made and even now (10K miles later) they are superb.
Well, for my single spark machine it had a significant effect on engine smoothness - particularly the surging. I'm not sure how much was down to "new plug" syndrome either but the bottom line is that I was really happy with the bike afterwards (and still am).
b.t.w. our local stockist is Clevedon Auto Spares.