[Stinger101]

Hi Gazza, You know I won't know about any clearance issues that are highly likely not to be there, but I can say that I don't think you'll feel any difference at all in normal road use. The difference in any ride height is negligible and shouldn't need any adjusting at the rear.

I say that because the original Yamaha R6 used to have a 120/60 but we all changed to 120/70 for track purposes and that's where speed of turn and feel are just as or more important maybe. We never felt anything other than supreme confidence as it always felt a lot better than any 120/60 item. Though that bike had a 180/55 rear already.
The 120/70 raised the front by about 5mm.
Well, that's my two penneth right there! :-)

As for slower steering, that's not an issue. The 120/60 has a flatter profile that the 70. The 70 will likely feel sharper as it happens.