None of those hybrids have been available in my area so I can't comment on performance. But I'd be very interested in growing the Walburton's Rosemary......my experience with other Tristram introductions has been very good. I'll keep my eye out for it.

And frankly, I am very flattered that someone of your reputation and experience with hellebores would look to us amateur/hobby gardeners here on GW for thoughts on why niger and x hybridus are so difficult to cross! I doubt any of us could tell you anything you don't already know :-) I am not a hybridizer by any stretch of the imagination - just an avid grower that reads alot - but it appears that neither of these plants lends itself to crossing with other species/hybrids. I've often wondered about this, as it seems most other species of hellebores cross quite easily.