The tubes I bought in the end were a mixture of Columbus Niobium and Columbus Zona .8/5/8 and .8/.6 for the seat tube Double OS. Fork is Columbus Minimal 1 1/8. I am over 6 foot and 170 lbs
I am building with a sloping top tube for a long exposed seat post length - I am sure this has a bit of flex.
I have had a few days in the workshop over Christmas and my jig and tube clamps are finished. The clamps took longer to make than the jig!! and I learned a lot about using a DTI and a 4 jaw chuck. I told my 11 year old daughter I was making tinsel :-)
Tomorrow I will make a couple of drum sanders for cutting accurate miters. Then I just need my lugs (on back order) to get started - and an Oxy Propane set and ........................