that's a good setup, but I think the inner cone may be contributing to the size difference.

You are not going to be able to feel a small difference in thickness, all the difference in feel comes from the diameter of the tubes. I just scanned an academic article about that yesterday, but I'm not sure where I found it. Don't think of it as being too stiff, think of it as being really solid.

I was regretting making the same choice in tubing size recently, but mostly because the resulting frame is going to be pretty heavy. I'm sure once I have it painted orange, it will be fine. But I'd rather have a bike made out of 1OS Spirit for Lugs. I am really horrible at judging frame stiffness though. Geometry is a different subject, I'm fairly sensitive to that.