There is, it's called the polar moment of inertia, I can't remember the exact equation but the diameter's contribution to stiffness is the diameter ^4 power. In other words, a littleincrease in diameter means a big increase in stiffness. I'm reaching back into my memory but I *think* someone actually calculated the difference and found from 24 to 25mm there was a 33% increase in stiffness and from 24 to 26 like a 66 or 90% or increase?

Either way, you wont' be able to get 75lb more load (Take 33% of the weight supported by the front end, that's the increase in weight you'd need to over come the higher spring rate and get back to the flex you have), you'd need say a .2mm increase in diameter.(I'm totally guessing here) However, this is not necessarily bad for if you use the stock bars you will get more flex with that front bumper. Which, unless you are into the fast stuff, is usually desirable.

Should no one pipe up about the added stifness I'll crunch the numbers when I get home.

Frank.