Purple elastomer pair in the LT is for the last threshold of acceptable rider weight on those.
I'm right around 200#, and so I got the Black ones on my Bike Friday Pocket Llama..
... perhaps If there is not much exposed seat post you will be OK.
the wall thickness is generous on the 27.2 tube part.
but like aircraft , the fatigue of the metal will have a shorter useful life
in higher stressed situations
The ST all the density ranges of the elastomers are the same color,
so you have to read the packet.#1 to 7 (special order is a #9)
[Max still tops out at 250#]
I got the PDF off the CC website they don't suggest rider weight over 250#
[black/black elastomer set]
and do specify it's a small bump reduction ,
you still have to get off the saddle for the larger shocks..
as read here:
http://www.canecreek.com/component-seatposts