I too am considering the investment banking route.
However, don't get blinded by the salaries. You have to look at the work hours.
Do you want to be working 100 hour weeks? Think of the effect it will have on friendships, relationships and family commitments.
Fairly frequently you will have to do 7 days a week, 14 hours a day. That could mean 8am till 10pm. If you have a family, how will you see your children? You will probably have to leave the house at 7am and get back at 11pm...
Is the extra 30k, 40k or whatever, worth not seeing your family??
I think the actuarial route seems better, considerably less hours, still amazing pay. Plus, I think the job security is much better. Actuary usually gets rated the #1 job in America, year on year. That is after taking everything (working hours, pay etc) into account.
Either way, you don't need to decide right now, do a mathematics degree (possibly some statistics/economics modules) and you will be well on your way into either job.
Obviously, IB would typically require a target university; Warwick, UCL, Oxford, Cambridge, Imperial or LSE.