yeah, afaik, the exploit on the 360 is using the wrong size address. it's in hypervisor 4xxx (can't recall exact number), so all jtag and rgh consoles use an old hypervisor. originally, you could just jtag the system to use, but it does have efuses like the switch, so downgrading wasn't possibly until rgh. that's not exactly downgrading but taking control of the boot sequence to allow for it.