Like mondeo, I'm a street shoe 12 (11.5 on the left) and I fit into a 28.0. Right foot is snug, but it loosens up as the liner warms. Personally, I think a 28.5 Krypton shell would be way too big for you if you wear a 10.5 street shoe, but consult a boot fitter to be sure.
+2
Same deal hear, size 12 street shoe and I wear a 28.5. I have a really wide foot so my shells required some stretching and grinding. Keep in mind that going up in size doesn't necessarily mean that you'll get a wider boot. And, no, my toes are not curled in my boots. I tried on some Full Tilts (not the Bumble Bees, not sure which model) when I first tried on my Krypton Cross's and found them to seem slightly wider, but the difference was barely noticeable. I think we could have made either boot work equally well, but in the end I liked the buckling system on the Krypton's better.
Remember that you can always make more room (to a point), but it's harder to fill in voids if the boot is too big to begin with.