Echinocereus engelmannii x E. mombergianus
Echinocereus engelmannii x E. mombergianus is a natural occuring hybrid in the wild. These have proven cold hardy to -2F in the garden but have not been tested lower. These should all get large red flowers. This hybrid has potential to be a very interesting hybrid.
I do not guarantee these in a zone 5/6/7 because everyones growing conditions are different but this would be a good trial plant to grow in your cold outdoor garden. Try to plant outdoor 90 days before 1st hard freeze.