Try them at 80, 90, 100, 110 PSI. See what you like the best? The best pressure depends on what your objectives are. The lower you go, the more cushy the ride and possibly better grip (until you go too low and pinch flat). The higher you go, you improve rolling resistance (until you to too high). At the end of the day, you have to balance the two. Me, I'd run them at 90PSI, but I'm not smallish.

How much do you weigh?

About 127.

According to the Michelin Tire charts you should be running just shy of 80 psi.

I figured... though I wonder how to weigh that against manufacterer's recommended minimum of 87.

As usual there are a lot of 'depends' for answers to these type of questions. You would need to know the actual width of the 23mm Schwalbe Ones compared to the actual width of the 25mm Veloflex tires. Also, are you putting these on the same rims? Some 23s are the same size as some 25s, and different rim widths will also complicate things. Getting that out of the way, the next thing to consider is your starting point of 90/90 with your 23s at your weight of less than 130 pounds. IMO, that's pretty high to begin with - maybe your starting point of 90psi isn't optimal?

The next thing is road surface - you are comparing your local road surface to Rotterdam. You'd need to factor that in for sure. If Rotterdam is a lot rougher, then you'd want to go less psi regardless of the change in tire size.

From my experience using the same tire model - 4000s 23s to 4000s 25s using the same rim on the same local roads, I'd use 5-8psi less. I ride my 23s at 80psi and generally ride the 25s at 73-75 psi. I'm 145 pounds.

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