This seems like a pretty rare tree still, even the main species tree.

FWIW, My main species tree has been slowly changing colors for a month now and still has some green. It gets a lot of sun and shows just a little heat and drought stress so I would guess the regular version could handle your version of summer with flying colors.

Good luck and post pictures!

less rare in the UK but Z4 would be pushing it well beyond the limits. Even in Z8, it prefers a sheltered position.
The RHS lists it as H5 - or equal to Z7a -6 (at a stretch). Suspect even the plain green would struggle.....but, if you have a microclimate, out of cold drying winds, it is likely to be root hardy with a good heaping of leafmould around the base.

MOBOT lists the species as zone 5 hardy. My species tree is perhaps 7 feet (2 meters) tall so watering it during last summer's record heat and drought was easy enough. During the record heat and drought mine had some droopy leaves which rebounded nicely after watering. It was a BAD summer though. My metasequoia lost 90% of its foliage and a good number of stressed trees died.

Our last couple winters have seen 0 degree F temps, zone 7 I guess, but nothing extreme that way. This year we had some late snow which did not seem to bother it.

Capanula, is the variegated form that much more tender that it is only zone 8 hardy? That is barely below freezing, right? I assume it tolerates sun less well but that is a summer problem.

Here is a link that might be useful: MOBOT