Something got me to thinking while I was airing up my tires a bit today...
When I was racing my Ninja 250 around Deals Gap a few years ago, I was filling my tires to 30psi (which was recommended to me for good traction), and out of curiosity, I checked my tires immediately after a run, and naturally the pressure was higher, 36psi to be more exact.
Which got me to thinking again, today. The rated speed on the tire is related to heat, if I'm not mistaken, and if one fills the tire to sidewall, then proceeds to drive at the rated speed, the tire would naturally arrive at a higher pressure after some high-speed driving. I can only imagine that the tire designers planned for filling a cold tire at 60-70F which got to 120 or so in the afternoon, while traveling at the speed rating... (This of course is merely speculation).
The conclusion this lead me to, though, was that a safe over-inflation could be extrapolated by traveling at the top speed of the tire after having cold-inflated to the sidewall pressure, then experimenting to find the cold inflation pressure that would cause the tire to arrive at the maximum pressure at some lower speed, in my case a tire designed for 110mph that is only used at say, 40mph.
What say all you more learned than I?
