Really? My RGH'd 360 never had issue and instaboots, but my case doesn't speak for everyone.
I also have a blades dashboard 360 (Xenon, of all models) at my place which basically has no uses.
Yeh, RGH relies on a glitch (non-reliable in nature) and takes some time to boot.
My Falcon RGH (first gen coolrunner, 0day install with unoptimised wire routes etc) does a single cycle 9 out of 10 times, the one times it takes an extra cycle to complete booting.
JTAG doesn't glitch the CPU, it's like a CFW PS3/modded Wii in that aspect.