What a Band 6 actually puts in, and gets
At the bottom of Band 6 in England, the payslip shows £326.33 a month for the pension at 9.8%. Because it comes off before tax, take home is only £261.07 lower than it would be without it. On top, the employer pays 23.7% of pensionable pay, about £789.19 a month. And each year at that pay builds up about £740 of yearly pension (1/54th of pensionable pay), which is then increased every April until you retire.
Contribution rates depend on your country
England and Wales share one scheme with six tiers from 5.2% to 12.5%. Scotland's scheme, run by the Scottish Public Pensions Agency, has nine tiers, and Northern Ireland's HSC scheme uses England's thresholds with higher rates. Employers pay 23.7% in England and Wales, 22.5% in Scotland and 23.2% in Northern Ireland. The full tables are on the NHS pension page.
The tier doesn't change what you build up
In the 2015 scheme everyone builds up 1/54th of their pensionable pay each year, whichever tier they're in. Higher earners pay a higher rate for the same build-up rate; that's how the scheme shares the cost.
Leaving the scheme
Opting out raises your take home by the real cost above, not by the full deduction, and you lose the employer contribution and the pension you'd have built up. Read opting out of the NHS pension before you decide.