Is the junior limit calculated on the minimum number of teeth they can have in the back, gear inches or roll out?

If it's either of the last two, you could run 50/34 (or 50/36) then 13-25 or 13-26. the 50/13 combination should give you 81 gear inches which is the same as 52/14. so you lose nothing in the bottom.

I personally race on FSA K-Force (both 50/36 and 53/39) and have never had an issue with them. I've used the 36 ring (FSA) on a set of Shimano R700's that I have also with no issues.

--brett