I'm developing a game that is using box2d physics pretty intensively and my beta tester reported sloppy performance when there were a lot of objects on the screen. I was practically always hanging with the DEBUG version of the app and had pretty stable 60 fps all the time. After fiddling with practically all the build settings I noticed that in the DEBUG build mode a flag `ONLY_ACTIVE_ARCH` was `YES` whereas in RELEASE it was `NO`. After building RELEASE version only for ARMv6 and installing it on an ARMv7 capable device, we had stable 60 fps. Trying to build for ARMv7 (Thumb) gave a sloppy (30 - 50% worse) performance again. There was also a slight performance hit visible in non physics simulated environments. The testing devices were iPod Touch 4, iPhone 4 and iPhone 3GS. Can you please share your opinions on why that could be so? I have no idea :)