Now, I just sit back and wait for Diane B. hehehe
. . . here I am.
The brands that usually bake at 265 (the Fimos and Cernit) can
be baked at higher temps (and will even be stronger), but they may darken a bit, especially if not protected while baking (by partially or completely enclosing them in/under something else**).
Convection ovens are excellent for baking polymer clay though, so if your convection goes down to 265, that would be fantastic. If it goes only to 270, that would still probably be better than 270 in a regular oven because the heat is so much more even.
Remember that just because the dial says 265 (or any temp) doesn't mean that the actual temp inside the oven will be that temp... ovens are notoriously off. So you'll need a cheapie oven thermometer no matter how you bake to check the actual temperature you're getting, possibly even in various spots of your oven. It's possible that when your dial says 270, it's actually baking at 260 or 280. . .
Or if you wanted, you could switch to a brand of polymer clay that normally bakes at 275 or higher (Premo or Kato Polyclay, or Sculpey--but Sculpey often darkens even at its proper baking temp and also isn't as strong when thin)
There are also other oven-y type things that can be used to cure polymer clay besides ovens, so you might want to try one of those if you get no satisfaction from one of the other things.
** info on "Other Ways to Cure Polymer Clay," as well as "Enclosed Baking" or "Partially Enclosed Baking" are here:http://www.glassattic.com/polymer/baking.htm