It is the same net result if both partners are earning over the 20% tax band (currently 44,000), so tax credits/cut off should be split evenly in my opinion.
Matters for pension contributions. Spouse 1 should reduce their credits to maximise their pension contribution relief at 40%. By how much depends on a) AVC age limits and b) their ability to make contributions.
Two relatively evenly matched pension pots are better for optimising tax credits in retirement than having one main “earner”. Also two tax-free lump sums is better than one.
Are you certain about this? Other threads here seemed to suggest doing it beforehand was necessary, although that might just have been out of caution rather than necessity. I’ll admit I haven’t tried it yet as wife was part-time until recently, so I’m not doubting you, just afraid of getting caught out!
Either person's pension contributions will reduce the couples marginal income by the amount of their contributions.
The limiting factor for the lower paid person is the maximum 9k of the 20% tax band that can be transferred to the higher paid person.
When the statement of liabilities is done it will calculate the total taxable pay for the couple. This total taxable pay will be reduced by both spouses pension contributions.
The only thing that will be different is that some of the lower paid spouses pension contributions might not be tax relieved at 40% at source.
Your wife can only get 40% pension relief on her earnings over 35k.