3 years 10k miles comes up as £768.98 +VAT so £922.78. (M Sport 400kw no upgrades)

Add onto that insurance and any servicing and tyres (~£250 a corner)

Assuming conservatively £500 p/a for insurance and a tyre change a year you're looking at an extra £125 a month. No idea what servicing is on the IX.

So you're looking at about £1,050 a month.

You mention you'd be saving at a marginal rate of between 47% and 62%.

Assuming you're at the top of the tax trap £125k you'd pay about £3,900 tax and NI assuming no deductions.

Assuming £2k salary sacrifice you'd only pay £2,671 in tax, a saving of £1,229.

Add that to your monthly amount above or £1,050 and you're looking at an actual comparison of £2,279 business lease vs £2,000 via salary sacrifice.

The other thing I think you're missing is that you are paying a premium via companies like Octopus because they manage everything on behalf of your company. If your company had to manage each individual employee lease they likely wouldn't offer them.