With the new frame, the choices of tires are "better" because of the extra width allowed at the swingarm. With the old frame, a 150 is about as wide as you can go without doing things to shoehorn a 160 in. From those I know that have done a 160, it didn't work out too well in the long run. I also know a couple of folks who had a 21" on their touring bikes and ended up back with a 19". The 19" is a good compromise between looks and performance, but that's just my opinion, and you know what they say about those...

I went through what you're going through when I put new wheels on my '06 SEUC. At that time, there was NOTHING in an 18" rear that even came close to the stock 16" rating, so I ended up with a 16" rear and an 18" front, with Metzlers on both ends. Looks like now they've got the 18" 150 at least rated up close enough to the stocker that I wouldn't be real concerned about it...77H and 76H are pretty damn close. It's tough to decide what to do when you're looking at spending some big bucks on wheels, rotors, pulley, etc. Then you need a flush mount front axle, better calipers...it never ends. I ended up with a chit load of money tied up in my '06...PM wheels, Pulley, PM calipers, Matching floating rotors on front, standard matching on the rear, Tires, axle, new rear brake line. It looked good when completed though, and it stopped a hell of a lot better (stock bikes didn't have Brembos back then). I got it all through HogPro and was very happy with their customer service and helpful advice.
That's another thought: Perhaps the new frame design distributes the weight differently front/rear.

Doesn't make sense though...can't see there being that much difference in weight distribution just in a frame design. Not trying to get you off track here, but the Dunlops on my '11 SERGU handle really well thus far, and seem to hold up well from what I'm reading. Also, I've heard good things about the Avon tires, but have not looked at their offerings for your bike. I really liked the Metzlers on my '06, other than the fact that the rear wore fairly quickly with my riding style. Great handling though.