Thanks duanedr

I am not really trying to solve a problem, just considering all the options.

I enjoy the design and learning process as much as the building and riding and since I cannot start the build for a good few months I might as well investigate different ideas.

For reasons already stated I am not that serious about going the ISP route, but neither do I want to just follow what everyone else does.

If I were to go the ISP route I would (at the moment) go for a 1.25 inch double butted tube .8/.5/.8 with the .8 section starting below the TT/ST join and going right to the top. However the longest tube I can find is way too short whiich would mean having both an ISP and a seatpost, which sort of defeats the object. :-)