The benefit really depends on the rate. When you get near the 1000/day range outside becomes far more lucrative than inside due to the flexibility it gives you

The benefit really depends on the rate. When you get near the 1000/day range outside becomes far more lucrative than inside due to the flexibility it gives you for tax planning, as you can defer personal income to a future date where it can be taken in a more tax-favourable way (eg via SIPP or BADR).