Example: If you really liked Kodak Tri-X 320, you can shoot Kodak TMax 100 @ 400, and then push develop in Xtol 1+1, agitating every minute, and get a very similar tonality. Or TMax 400 @ 1250-1600 and do the same thing. It's very difficult to tell prints from one or the other apart.
This is why you need to test. Shoot a roll at 200, and cut in thirds. Process in D76 1+1 and adjust until your prints look like what you want them to look. When you push process, the thing you really have to look out for is backlit subjects, especially portraits. Details in dark shadow of someone's face easily gets lost in deep shadow, important details like eyes.
If you have the ability to bring two cameras, use the Foma 400 for difficult lighting, and use the ISO 100 film for well lit occasions. Again, bring the largest aperture lens you have. In the winter I almost always employ a tripod, simply because there aren't that many moving subjects around, and then it doesn't matter if I shoot ISO 100 or 400. But traveling with a tripod is a PITA sometimes. I recommend Feisol carbon fiber models that are highly compact for traveling.
Finally, what's stopping you from ordering some 400-speed film to be delivered to Sweden?