HR should be a lot lower in training than in a race
Don't really agree I think it depends on what you are trying to improve, a training plan should cover a variety of aspects, including flat out efforts during intervals or race simulations which should be as close as you can get to your race output and you should be able to see your HR max (if not you simply aren't pushing as hard as you can go...). You also need to focus on base training at lower levels etc.. depending on your phasing and your current targets.
As mentioned HR is a yardstick rather than an exact measure as it can be effected by many things. But I do feel it is a good thing to know what your sustained maximum average HR is over a time period, it gives you a bench mark and you can adapt from there. As you get fitter those numbers may change, I haven't seen this personally, I've just got faster / more powerful for the same HR averages.
My current bench marks are approx:
202 max (I have seen 204...)
190+ for bursts of less than 2 mins no more the 10 efforts or I risk cramp
178 for upto 90mins
168 for upto 120mins
157 for upto 6 hours
150ish for 6 hours +
But, very subjective depending on health, when I last trained, fueling, hydration, weather, etc...
You just need to measure and record so you can build up a picture
I'm saving up for a power meter...much more useful for this sort of thing. Shame they are £££s