I think that sounds like too high for too long. You might talk to the instructor. The good ones will provide some information about this. Yes, when I first started I would blow up at some point, and woudl have to slow down. For me, the trick is a sufficient warm up, then you can do a lot more without blowing up. When it does start, you should definitely back off. I agree, it gets 'better but not easier' because you compensate by cranking it up more. For me, it does definitely help, especially with sprints and hill work.