In my younger days when my quads were more massive, I used to tromp on the cranks on my 531 butted Atala, and yes, the bb did flex, and with non-indexed dt shifters, you had to have the front derailer set just right within it's range or it would be scraped by the chain. But I learned to pedal at higher revs and drop a gear or two, and frame flexed less. Also, despite the flex, 100mile + rides were not exhausting, and IMHO frame flex is not indicative of poor design.

A neighbor is trying to get me interested in a Dedaccai Griffe in my size that he has... but I'm hesitant partly because I don't feel the need for another bike, and partly because if/when I do get another bike, it will be steel, and i'll most likely spring for an oversized tubeset such as the EL-OS or such ilk. May be a pipe dream for me with the arthritis becoming more insistent.

Anyway, my three cents: consider modifying your riding style, don't dismiss a frame that flexes, and perhaps seek out a more modern steel frame that would be less flexible in the bb. Unless you're going to limit yourself to shorter rides, too stiff a frame can result in a less happy experience.