I went to a 160/60 and I think it's great. The stock 170 on a 4.5" rim was way too wide. The 160 still provides me more than enough traction to lean over to sidestand-dragging angles... no problem.
BTW, Avon makes a version of their 160/60 AV36 rear tire specifically for the 4.5" rim. I think the Avons work great on this bike - they are bit touchy when they are cold, but totally predictable. I've got ~8,500 miles on my current set, and just placed an order for replacements. I'm running the new Metzeler Sportec M1s on the Ducati, but decided that I really like the Avons on the V11S, so I'm sticking with them.
__Jason
00 M900Dark
00 V11 Sport