Texensis variety with the largest flowers

Hi,

I'd like to try a Texensis with tulip shaped flowers. However, one website I visited stated that the flowers of the Princess Diana cultivar are only 2" long. I think Gravetye may have 3" long flowers. Which of the following has the largest flowers -


Gravetye Beauty
LadyBird Johnson
Duchess of Albany

Thanks

Hope this helps:

Gravetye Beauty http://www.clematis.hull.ac.uk/new-clemdetail.cfm?dbkey=527
LadyBird Johnson http://www.gardenimport.com/spblvl3.php?lvl=Clematis&nm=LADYBIRD_JOHNSON&ref=CL4675
Duchess of Albany http://www.gardenvines.com/catalog/clematis-duchess-of-albany-p-258.html