What about if I connect the HT-5 to a 4x12 cab, is the ID60 still more loud?
If you have a 1x12 cab and a 4x12 cab which are loaded with the same speakers, the 4x12 cab will sound bigger; more like a "surround sound". But not essentially louder than the 1x12 because they have the same speaker (with the same decibel and efficiency, etc). It's still a 5-watt amp driving those speakers.
On the other hand, the ID60 would be around 60 watts of power driving its speakers. More clean headroom as you turn up the volume.
I've tried turning an HT-5 combo at full volume, even tried plugging it to my 2x12. It was really loud for a 5-watt amp, but still tolerable when you're quite near.
I have not tried the ID60 at full volume but a few friends use them at gigs without mic'ing, so I guess it can deliver on it's own the (clean) volume needed at those loud applications.