A couple more points: First, testing with a grain focuser might or might not produce the same results as testing with actual prints. For one thing, grain focusers don't generally tell you much about edge sharpness. There might also be effects in your visual perception that result from the decreased brightness as you close down the aperture, but those wouldn't be the same as what the paper "sees." Thus, although the grain focuser may produce a useful "quick-and-dirty" test, I wouldn't rely on it if you want to determine the very best aperture to use. (There was another recent thread on this topic, though, and my position isn't the only one, so do a search if you want to find other viewpoints.)
Second, the differences between most of the apertures on a high-quality lens like your Componon are likely to be slim. I don't own a Componon, but tests with my two best lenses (an EL Nikkor f/2.8 and a Vega-11U f/2.8) reveal little in the way of differences in center sharpness except at both of the extreme ends of the aperture range, where it drops off. Edge sharpness tends to increase with smaller apertures until close to the very smallest aperture, and this effect is a bit more pronounced, but still not huge except at the widest aperture. Overall, you'll probably be fine for any but the largest enlargements or most nit-picky criteria at anywhere from f/4 or f/5.6 up to f/11 or possibly even smaller. Of course, if you've got some time to spare there's no reason to not perform the tests to determine what's the absolute best aperture....