Mix 31 will cover the lower amateur bands as well as 10/11m. 43 performs better from 10 and up, how high up, I do not know. I know this is vague, but I am not a ham, I'm strictly CB only. I don't even use UHF.
The other reason for #43 in that particular ferrite is availability, #31 is harder to source. Unless the ferrite fairies just delivered some for Mouser. By the way, the price of those has gone up dramatically, I previously bought them for under AU$7. Must be covid and the shipping the container crisis. Look at Element14 instead.
If you want to know how they perform at various frequencies, try YouTube. I believe there are some videos testing baluns and ununs using different mixes. The SWR curve may be directly relative to choking impedance??
The other way to find out is to read the article I was talking about. He did some fairly extensive bench tests, and there's a table on ferrites and windings for each band. The number of windings is frequency dependant, more windings is not better for optimum choking impedance.
I'll dig up that link, it's a must read for all radio operators.