That's a tough workout. I boxed in an amateur exhibition a couple of years ago after training for about three weeks. It was only 3 two minute rounds but we were two heavyweights going all out and I was sucking for air after every round.
Yeah, it definitely kicks my ass. I lower intensity if I have to and when called for. Sometimes the body can't go like it used to even at 24.
High Intensity might be misleading. I go all-out as best as I can, but probably could go just a touch harder. So I would say...80-85 percent exhertion. I need to start monitoring heart rate to see.
I'm just afraid you're being too hard on your elbows by not being close enough to the bag or by locking your elbows out too much. I'd hate to see you get hurt or discouraged.
I've been doing this a LONG time and even I still get soreness in my elbows....mine is more from 'hyperextending' my elbow when sparring, and I think it is when I try more of a 'quick' snappy punch (rather than digging in).
You might be a little too far away from the bag when your working out.