If one is North of the Mason Dixon line, with several months of snow and ice, snow tires are likely worth the expense. If you are South of the line, in Texas for instance, they would be useful about 1 week a year. The safest tires for Texas are tires that won't leave home until that week is over. I don't go out because of other drivers and most importantly because the roads are treated with sand and a salt slurry in DFW area.
Much of getting around 'safely' in the winter regardless of ones location has to do with driving style and ability. In most circumstances slowing down, planning to stop earlier, slow acceleration and backing off more car lengths than usual is enough.
In all the controlled tests I have read winter tires are best for snow and ice and in some circumstances wet roads. The more severe the weather the greater the benefit.
All weather tires are a compromise for both summer winter driving. However, I see no value or benefit of running summer or winter tires on an X5 in Texas. An X5 is a good handling SAV but is not a sports car. I can scare myself enough on all season tires in the summer and having the ability to go faster around curves with an X5 would only make a danger to myself and others.
Here is one controlled test on ice:
https://www.motortrend.com/features/...ires-worth-it/ Note that even controlled data varies by vehicle. Even sticking to only X5s, which is the best thing to do here, engine and electronics associated with handling, acceleration and stopping by year will vary.