About a month ago I slid the tubes up 1" in the clamps on my '03 B12N. The only difference I've noticed is quicker steering/response and need for headlight adjust. I've run it up to 120 a few times with no slapping or even a hint. Lately though I've felt an 'oscillation' in fast sweeping turns...might be the Macadam starting to cup though.
If Ayers manages to ever get the 11" tubes to me, I'll be mounting the Pro-Tek clipons meaning I'll drop the clamps an additional .4-.5" Ed tells he's had no problems with slap with his S with the Pro-Tek dropped 1 1/2".
I'm seriously considering a dampener though as an added preventative. I once had a serious slapper lay me out at 110mph and it comes quick and there ain't nothing you can do about. Don't want to go there again!