Now I know that HCS, Biggrim in particular has stated many times that there will never be an epic set. That is not what my suggestion is for, well not really.
I was looking at the auction house earlier at some of the items and while I'm happy that some are available for lower levels, it does mean that anyone high enough to wear ALL of the Hunted Cow epics will be hampering themselves with inferior items. (stam/xp gain wise)
Would it be possible to create a unique set bonus for these items, that gives no battle stats, only stam/xp gain increases and also does not enable SH/CoA/CoD etc. (although the buff would be virtually useless to use on them anyway)
Now, failing that as I can already sense the, "We've said multiple times there will never be an epic set!" statement incoming...
How about a new enhancement that adds the stam/xp gain but only works at certain intervals?
So each item could give 12% to this new enhancement with bonuses coming in at 24% and every 12% after?
I realise this seems like a lot of work for just a little extra stam/xp gain but in my mind these new HCS epics should be, well, you shouldn't have to take a hit in your stam/xp gains to wear them.