QEMU does not emulate cache behavior, other than a few status registers.
It's probably safe to perform these tests on the camera. However, at this point, you'll need some help from us to sign the binaries you want to run (currently the binaries can be run either as autoexec.bin or as FIR; the former needs a boot flag set in the ROM and the latter must be signed). To my knowledge, CHDK had trouble running the Canon firmware from a firmware update on most (if not all) digic 6 models, so we might have to enable the boot flag from the bootloader context, in order to run autoexec.bin. Traditionally, we enable the boot flag from main firmware, but we did enable it from bootloader on VxWorks models. It's probably best to try on a less expensive D6 model first; if anyone is willing to take the risk, I can prepare a FIR for enabling the boot flag in this way.
Having some other ARMv7 device to test things could be helpful, too.