Interesting...On the other hand, I don't think I've ever used top speed on any of my cameras... I've always wondered why my RB lenses top off at 1/400th...
I have tested dozens of leaf and focal plane shutters of all kinds from brand new Hasselblads to old Copals, just CLAed Compurs, Nikon SLRs, TLRs, etc. using a timing test. No large shutter - even new - will ever hit nominal speed with a simple shutter speed timing test.
There are several reasons for this. The time open in the center is longer than the time at the edges. Unless you have a timer that takes this edge-vs.-center timing into account, measuring just center open time naively will give you an apparently slow shutter.
The other reason is just physics. It's easy to tune a small curtain on a Nikon or Leica to be pretty close to nominal. But when you're slamming around the big shutter blades on a Copal #3 shutter, it's hard to move that much mass with any real timing precision.
For this reason, if a simple timing measurement show the higher speeds up to even 1 full stop slow, I don't worry about it. It's inevitably a measurement artifact (that's "artefact" for our Brit cousins

- unless you have a fancy lab speed tester. More than that, and the shutter needs servicing in my experience.
The good news is that the shutter center speeds are
slower at these higher nominal speeds which means more exposure. For monochrome film, it's just a non issue. These films have more than enough latitude to handle it. For color some testing may be in order to see how the shutter is actually impacting film exposure.
I would point out that our predecessors managed to work with far lower precision tools than we have today, but had such mastery of their craft that they learned to work with the equipment they had. All they needed was for the error - whatever it is - to be
consistent. And that's the one thing that will send a shutter out for CLA - if it cannot consistently deliver the same measured speed, even with a simple timer.
Some slight variability is expected, especially with older leaf shutters because the springs get stretched each time you cock the shutters. For this reason, when I test, I always measure the error across 5 firings, expressing the result as error in f/stops and I keep track of the standard deviation across the measurements. A high SD means a grumpy shutter. In the field, I always prefire older shutters before actually exposing the film, to get the springs going a bit.