Good thinkin' replacing them both.
For scrubbing in I go to a empty parking and start out slow doing figure eights. After about 10 or 15 minutes I increase my speed and decrease the radius, until I start grinding both footpegs. By that time the tire and nice and warm, so when I start dragging the valve covers, and the pegs are worn down to stubs I know they are scrubbed in properly, and are ready for the Chicago streets. I have to get new footpegs when I change tires, but I've found some aftermarket replacements for about $25. I used to do circles, but one time I threw up in my helmet, so I changed to figure eights.
Eventually I end up with no chicken strips front and rear...
Just kidding! (pain pills OK?)
I just take it easy and do S turns like NCGS said, when the roads allow. Really though the Syncs don't feel that slick when they're new, like other tires can. Maybe because they're Silicon based tires and/or they don't have that resin coating. The last change I did it rained right after and they didn't feel slick at all, they felt the same as worn in one's do - very good wet traction.
I know this because I usually test out my traction (with throttle/brakes) when it rains and I'm home. The city street's traction when wet changes greatly depending on how clean the streets are. When it's been a while since the last rain they are quite slick at first when it rains, compared to if it just rained a day or two ago. So I check it out...
Just a thought, I'm not saying you don't need to scrub them in... don't end up like me. Just saying you might be surprised how confident they feel shortly after mounting them.
It will be interesting to hear some other opinions about the Syncs'.
Mark, I see you bought the hugger you've been talking about, how do you like it?
Any chance you will make the show in Chicago this coming Feb? 
