The frame could be adding to the perceived flex as well. I have the bottom bracket installed in a Bianchi Ti frame. In terms of weight, I'm a 170 pounds plus or minus 5.
The tubes on the frame are huge, and the ride is quite a bit stiffer than I remember my previous King Kikapu being. I was hoping that this would rule out the frame being the cause. I plan on using this bike as my pavement trainer so it'll hopefully getting some throttle quite often.
I guess my concern aside from flex would be durability. Will the bottom bracket spindle be able to handle a noticeable amount of flex without breaking? More importantly, should I be concerned?