Depends on your frame of reference. The shorter tire will slow the steering, however little; 6mm lower in the rear as you know (15mm down from your 150/70); and effectively shortens the gearing by 6%. Some might see one or more of those as a problem, others not. Depends on what you can tolerate and how you use your machine. That said, TrailRider comes in a 160/60, so avoid all three conditions perhaps?