Crikey, I think I'd walk up that, heart rate limit or not! And the bloke at the front is hardly the best physique for steep climbs! On that gradient you'd have to be a skinny bugger to cycle up it.
I find really steep sections very scary, anything above around 15-16% and the front wheel starts to come off the ground and I worry I won't get out of my clips in time to get a foot down. Doesn't help that I'm hopeless standing up (and it puts my heart rate up), so I sit the entire way, taking weight off the front. Once I started cycling up it, I'd be pretty much committed, as stopping is very likely to result in a fall...
That's why I liked the climbs on bkool, safely bolted into the KICKR I could sit and grind up pretty much any gradient it could simulate, and no matter how slow I got it wouldn't fall over! In real life, I'd be laid on my side looking up at the world as it went past...