There is no gold standard. One can say a headphone that has a frequency response closely following a specific standard then that headphone adheres to that standard (say Harman target).
Any headphone that complies would sound tonally correct (if one finds the Harman curve tonally correct)
The K371 is relatively close, the Stealth is even closer, the HE1 is also close.
So... in the cheap range the K371 could be the cheapest headphone having a correct tonal balance and could be called a standard.
But is a closed headphone with build issues, pleather pads and has seal issues.
In the expensive range the Stealth could well be the gold standard. But again seal is an issue and is closed which one may not need.
It won't sound like a HD800S but will have some of its better qualities (have not heard one)
The HE1 could well be the gold standard but one has to pay a lot of gold to get it.
But not only the tonal balance matters. Some say that is indeed the case but it isn't. Comfort matters, seal matters, stereo imaging matters, build quality matters, support matters, open/closed matters, portable or desktop matters.
The HD800 is not close to Harman but is excellent at other aspects.
The thing is tonal balance is easy to correct, other mentioned aspects are not.
So the best thing is to buy something that is excellent overall (not seal dependent, comfortable, excellent instrument separation and does not need much EQ.
The HD800 (in the $ 700-1000 range) might well fit those criteria for a lot (but not all) people.
In that sence it is a good choice but (IMO) needs EQ to really become one of the best, at least for me.
Basically.. in every price range there can be a 'best' headphone but may not be the same one for everyone.
For me, in that price range the HD800 is the best choice. Others will claim the HE400 will do the same after EQ (it does not but to them its good enough).
Audition it, use it with EQ (or the treble filter when this is the only downside for you) and enjoy it knowing it does not get any better than this.
I have many headphones I like and use but the HD800 with EQ is the best. Mostly I can take a step back without being bothered by it and mostly use the HD560S (a good compromise but feels cheap and lower treble is too high but fixable)