I've got overclocked PCs and non over clocked PCs. One I've overclocked by as much as 50% - Opteron 165 CPUs are great for doing that. I've been overclocking systems since 1993, starting with a 486DX-33 overclocked to 50MHz, which was huge at the time.
Anyway, in my opinion it isn't just going to cook your system. It will either work or it won't. So long as you have your box backed up all you would do is format the application area, reinstall the firmware, and restore your channel and satellite lists.
I've done a 20 minute test playing a 1080p h264 DTS movie via NFS on the Azbox. No, it's not a very long test. Probing the board with a laser thermometer the CPU is running at 44.6 Celsius, which is a smidge over 112F. This movie would previously skip, pop, and checker. Gone with hardware acceleration.
In most cases of overclocking, if it's not going to work you'll know in the first few minutes. After that, I don't know if you'd notice on an Azbox because there are minor things that need you to hard reboot from time to time anyway.
Just my opinion. Your mileage may vary.