Couple things:
1. You should have waited with the bore until you had the pistons. Typically, the cylinder is bored with pistons in hand so that accurate piston-to-wall clearance can be bored. Every piston is slightly different in size. As it sits now, you may have too small a bore and need to hone it to get to the right tolerance. If you don't, you might seize the engine. Or it may be bored too big already, in which case you'll need to go to the next size up.
2. WSM is not the only company making .25 over pistons. There's Art, Wiseco, Pro-X, Yamaha, and probably a couple of others.
Bottom line: When you get the pistons, have a machine shop measure the piston-to-wall clearance and make damn sure it's within the specification written on the box for the pistons.