You can shove the 280 on the stock wheel but it is not recommeded. Metzler does not recommend it either. The tire will not wear properly, it will not look right, and there is a danger of it breaking the bead in some extreem conditions. That being said, I know guys that have ran the 280 on the stock wheel and had no problems..... other than abnormal wear.
I now run the Metz 260. The difference going to the Metz260 from the Dun 250 is night and day. The Metz handles MUCH MUCH better.......... in my opinon. The Dun is flatter in the middle, where as the Metz is rounder. You do not have to "push" the bike into the turn like you have to with the Dun. I have heard the Metz is much better in wet conditions, but i have not ran it in the rain yet.