UPDATE
I've every kind of RD-6700 that exists currently being shipped to me. So, no limitations there!
I've decided to use the RD-6700 GS (long Cage) and the Tiagra CS-HG500-10 11-32 Cassette.
This combination is well within the "Capacity" spec (40 is spec) and two teeth over the "Max Cog" spec (30 is spec).
By all accounts the RD-6700-A GS long cage will be fine with this. Plus I'm comfortable pushing the spec a little, now knowing exactly what/where I'm pushing it.
New Subject - what If I want even more T's.
I've also found a $20 device made by Wolf Tooth called a Roadlink.
The Roadlink does not increase the Capacity of a derailleur but does increase the Max Cog size.
My 50/34 cranks take a capacity of 16
The RD-6700-A GS has a capacity of 40
40-16= Leaving capacity available for the cassette not to exceed 24
With a Roadlink could actually run 11-34 (23 capacity) and still be under the Shimano capacity spec.
I've not purchased a Roadlink, but it is an option should my chicken legs require additional help.
BTW - their website makes great reading!
All the best
Barry