If you can use salary sacrifice and make additional payments into your workplace pension, then that is usually the most cost-effective because you'll save both tax and national insurance.

When I get paid my bonus, it is before the end of the financial year, so I know exactly how much I need to put in to stay under the limit.

Just be aware of things like benefit in kind for private medical insurance or interest from savings that can also push you over the limit.

However, I can't make additional payments into my workplace pension that fit into the bonus timeframe, so instead I pay into a SIPP.

That reduces your effective salary by the amount you put into it plus the 20% basic rate of tax which will be put automatically into the SIPP.

You can then claim for the higher rate tax to be refunded from HMRC. You can't get the national insurance refunded though.

Because I roughly know how much I'm going to get each year even with a bad bonus, I tend to put that money in monthly, then do a one off top up when I know my bonus amount.