Comparing Fish-Eyes : Rokinon 7.5mm vs Zuiko 8mm (FOV and look)

Indeed. Fortunately, a bit of defishing can help here too. Here's an image of Uppsala Castle with my glove figuring prominently in the lower left corner.

But defishing to Panini suffices to get it out of the way.

This is a pretty weird building, at least from this angle. As you can see, the castle is designed to have two wings but the left one was for some reason never built. It looks better and more impressive from the other side, where it sits majestically with both towers visible, on a ridge above the rest of the city.

You are right about that. One thing I did early on was to find out exactly where infinity is located (by taking a series of test shots of a target practically at infinity using slightly different focus settings). With this lens (as with some other more recent ones), there is no reason to think that infinity focus is exactly at the infinity mark on the focus ring (i.e., the manufacturer prefers to leave a safety margin up to the hard stop).

Now one difficulty in setting proper infinity focus, once you have found it is that, as you point out, there are no marks on the focus ring between infinity and 0.25 m (which is already way too close for most subjects). Fortunately, however, there are ribbed sections on the focus ring. Moreover, one of these sections is just around the infinity mark and can be used as a substitute for focus ring marks. One of the ridges is pretty much aligned with the infinity mark. I found that the next ridge to the left (when you look down on the lens with the camera in front of you) corresponds to infinity focus (on my copy, not necessarily on others). The next ridge corresponds to a focus distance of about two meters and the point inbetween to some five meters.

Another plus when it comes to focusing is that the focus ring is very stiff (although it moves smoothly). So once you have set it the way you want, there is very little risk that you accidentally move it.