The flex would depend on the tubing diameter...like any other material. Aluminum is not inherently a stiff material, it's stiff because it's usually massively over sized. Older, smaller diameter aluminum tubes were springy as all get out. Typically ti tubes are wider than traditional steel tubes, which compensates for the material differences. I weigh far too much right now and I LOVE my Merlin and Titanio. The Litespeed built Look, not so much.

I know others disagree with me, but I think that the difficulty working with titanium means that I would stick to brands with very good reps - older Merlins, Lynskey, Moots, Seven, Serotta.