My Icon is running with my backup restored, with Cortana on, location services on, everything the way I ran with 8.1 and the battery life is on par with 8.1. Far cry over the last build. Now Gabe did say that the Cortana bug may affect users, which means it also may not. My route was 10536>8.1>Restore backup>Denim>10549. No hard resets involved. I did let my phone do all of its background stuff, once 10549 was loaded, during the night while I slept; i.e. I didn't mess with it until it was completed.
So far this build has performance close to 8.1 with a few bugs here and there, at least for me. YMMV.