Aviva Workplace Pension - My Future Focus Long Term Growth S6 - Switch Over Advice?

Hi all

Via my workplace pension I’m currently invested in My Future Focus Long Term Growth S6, looking to switch this fund as 1) it’s the default fund and 2) I’m wanting to maximise my returns.

I think I’ve shortlisted two funds via the below split - but I’m unsure on the UK exposure part… my questions are what do you think, do you invest similarly to the below and what do you think to UK exposure? Also does it really make a difference when I switch the fund over from one to another, or not so much?

• 96% - Aviva Pensions BlackRock World ex-UK Equity Index Tracker S6
• 4% - Aviva Pensions BlackRock UK Equity Index Tracker S6

For reference, I also already invest privately, via a Stocks and Shares ISA, into the Vanguard FTSE Global All Cap.

Thanks!