I always go down one size on front and rear unless I have a 16 inch rear wheel, in which case it gets a 150. My Savage has a 100/90-19 and 140/80-15 stock set, the new front is a 90/90-19, and while I have a perfect 140/90-15 rear for it, I'm going to order/run a 130/90-15 rear instead. Seriously improves the feel while turning or in twisties, faster response to steering inputs. Slight on paper, but very noticeable from the seat.
Going one step larger in the front makes the bike feel sluggish. If it will even fit, usually you'll find a bit of interference with the fender bolts. My 63 CL arrived with a 4.00-19 front, a 4.50/4.60-18 rear... both with the edges of the tread blocks chewed up. It will be wearing a 2.75/3.00-19 and a 3.00/3.25/3.50-18 rear when it is back in service.