I recommend avoiding the Swix "universal" waxes. I have some "green universal" wax, probably 7 or 8 years old and it is complete garbage. Claimed temp range is +25 to -4 F. I have yet to determine in what conditions this wax works well, but at 15F on new snow it is some terrible wax.
I also have some Swix "red universal" wax. Claimed temp range is +36 to +10F. This is "mostly functional" wax but I think the lower limit it 20F. There have even been times when I felt this wax was fast.
For most conditions waxing really isn't necessary (in my opinion), I do it from force of habit. Possibly this opinion was formed as the result of using Swix universal waxes. Wax becomes very important in the spring when the snow gets sticky. Particularly if you ski on telemark gear.
The Swix website is terrible! What is the difference between F4 and UR? I don't even see the PS series on their website! Is it a current product? I am looking for a document which explains the various Swix products but I can't find anything. When I go to the Swix home page it appears they are only a clothing company. I conclude these people are idiots.
I am very happy wax companies are getting away from fluorinated wax. I believe the EU has outlawed fluronated wax. The US is terrible at regulating health hazards, and in Salt Lake City we drink all the fluronated wax deposited at the ski areas.