Nice pictures tim. I think we converse on another forum or two.
This is certainly a promising hybrid...there are various out there in the hands of a small group of collectors. Some time ago I saw a website with pics of various hardy (obviously) hybrids being grown in Nova Scotia, such as BVT X rex. Hopefully they become more obtainable through typical commercial sources like Rarefind.

Hi David

There are a few nice hybrids available through the ARS seed exchange which can be purchased on-line. I have another 10 types sprouting now under lights.

I traded with John W of Nova Scotia and received this seed

There is a lot of rex genes in this hybrid some of which look very interesting. Here's one seedling which looks like a young rex.

This one is from the same seed batch but has a totally different look.

I really like the combo in this hybrid which is producing long, narrow leaves.

Some of the Asian cloudforest species have the longest leaves of any tree I believe. The protistum X grande hybrids at Berkeley Botanic Garden are probably "only" 2 feet long at most, but truly surreal looking and I wish I'd taken a photograph of them with a soccer ball to give a sense of the scale. The flowering trusses must be roughly the size of a soccer ball. (of course we are lucky in the east to have one of the biggest leaved deciduous trees, Magnolia macrophylla; they don't always look great it gardens though)

A few update photos

R rex hybrid from John Weagle seed

The other R rex hybrid from J Weagle seed

R makinoi x rex hybrid

R hardy giant x mac hybrid

Another R hardy giant x mac hybrid

Wow, I'll have to get cuttings from you some day. Very nice.

Its great seeing the variation between seedlings of the same cross. Only time will tell which ones will be best

Wow! Very impressive. Maybe more of the traits of the putative rex parent are appearing in the F2 cross. Main thing I'd worry about with such a cross here is heat resistance since it is only 25% fortunei, but it should be just fine for you in that respect.

I'm worried about hardiness in winter since Hardy Giant really isn't that hardy. That 25% fortunei is not a big contributor to the hardy pool. I have 10 to 15 of these, only time will tell which ones will be hardy. Currently 4 are planted in the garden.