How much does ib/A levels overcap matter

As above, higher grades/predictions certainly won't hurt, but it is rarely as simple as "better grades = higher chances of offer". More competitive course tend to take more factors into account for offer making.

Do you mean - am I more likely to get a Uni offer if my predicted grades are higher than the stated 'entry requirements' for that course? Simple answer is yes, probably - BUT Unis look at much more than just your grades, so no offer is ever guaranteed whatever predicted grades you have. One choice just above your predicted grades is recommended - you may get an offer - but make your other choices more realistic, and include at least one choice well below your predicted grades as your potential Insurance choice.

Ok thank you, I was looking at data on uni of Warwick for PPE and Nottingham and wondering because neither have tests

I would say for pure Econ, they almost certainly have some weighting between AL's, GCSE's and your personal statement. PPE is probably a shade less competitive, but again they may take other factors into account.
So long as your predictions aren't wildly over-estimated, then they certainly aren't going to harm you. It's just a bit of a fallacy that once you are expected to meet the typical offer, being predicted higher must guarantee that you have a better chance. It may literally be a tickbox that you meet the requirements then they look at your PS for example.