Originally Posted by seejohnbike

Don't hold me to this, but i think it's not so much the crank/bb interface, as much as what the interfaces allow. As long as your cranks are held securely in one place, the degree of performance or flex is going to be attributed way more to the physical properties of the crankarms themselves and bottom bracket spindle.

for anything with standard internal bearings, you're just looking at upgrades to the alloys used in the crankarms or bb spindle.

For outboard bearing bottom brackets, the gains start to compound. Using an outboard bearing bb allows the bearings to be larger, thus allowing the bb spindle to be larger in diameter. This translates into a stiffer bottom bracket/feel to the cranks. (which can of course be used in tandem with stronger alloys)

also, a larger bearing diameter means the bearings themselves will spin slower (yeah, one revolution is one revolution, but with greater circumference, the tangential speed of the bearings themselves will be slower, math, math, math etc) which, iirc, means a little less parasitic drag from the bearings themselves.

i think this is in the ballpark, but if someone could confirm, that'd be great.