much better to look at
a) what the best uni you can get to is with your grades
b) what the differences between your 5, 6, 7 shortlisted unis are for the course you're interested in
you're asking for an abstract answer to what is a very specific and practical question
How big is the difference between universities ranked on the top 10, 30, 50, 70, 100
They methodologies are rather poor imo and the underlying data is even worse.
These league tables dont well represent employability or subject expertise, instead they are essentially an indexed moshpit of somewhat representative data.
I'll always recommend drawing up your own set of factors and do your own research on these factors specifically.
I think it is better to judge universities by their entry requirements rather than league table rankings. A university that has AAA entry requirements for most courses will most likely provide better education and prospects than one with CCC entry requirements.
There is only one subject that actually has all its graduates doing national exams after graduation AFAIK. Comparisons are hence very challenging.
There are definitely unis which take deliberate advantage of this though, asking for high grades purely to attract good candidates, then going into clearing later.