That is a very useful observation, and thank you.
One thing that became obvious last year is that the precocious gene has to be reckoned with when starting your plants for an appropriate plant out date. I had to advance my date unexpectedly because Kimberley and Beaverlodge Plum had started to flower while still in a beer cup. That was okay for last year's plan to test cold tolerance, but not the best plan overall, especially this year which looks like a late spring.
This year I am deliberately waiting longer to plant any varieties I know have the precocious gene, including the F2 of your KimberleyXEPB cross, to make sure that the conditions are fit for planting when they need to be set out. It is the reason for posting this question, too, because so many varieties are new to me, I don't know from experience which ones should be planted later.
Your comments elsewhere about cold tolerance are correct in my estimation, that the capacity of many 'early' tomatoes to produce in early spring conditions is limited to at best a narrow "cool" temperature range not much below the 'goldilocks' zone. Kimberley did produce a few early fruit, followed by a big gap: the main crop came in at the same time as Stupice. There was really no advantage to stressing the plant with temperatures below its tolerance.