I guess it depends if you’re trying to reduce your taxable income then a longer period might add up.
embarrassingly I don’t know what my lease interest rate is, or even where to find it
Don't be too concerned about any 'interest rates' you were quoted, as this is a lease not a loan, there is no 'interest' and so there can't be an interest rate. You can work out an 'effective' interest rate, but if you're just comparing to buying outright with cash or a regular car loan - you don't need an "interest rate" to do that.
And any so called "interest rates" can be calculated however you like, and can't be compared against other quotes - people may find they had a so called 10% 'interest rate', asked for it to be lower, and their '9%' rate was actually more expensive.
When comparing, it's the 'lease' or 'rent' amount - a $ amount - you would be comparing.
An example from Toyota Fleet Management - the "Rent" (and management fee) is the number you want to compare, not the "interest rate".
If you're curious, there are spreadsheets like this
EV Novated Lease Calculators (posted in several Facebook groups) that can help you compare against your other options, and find an "effective" interest rate.
And remember that the amount financed - ie the car purchased price, will have the "commission" and other establishment and other fees, "profit" (nobody will rent you something for nothing!), but potentially other things too - like the "ECO Protection Pack" mentioned earlier, but also things like some add on insurance (redundancy protection, total loss etc) - which then all factor in as part of the "rent" amount.
tl;dr forget about the 'interest rate', as it can be whatever they want it to be - focus on the actual rent amount when comparing against other quotes (and remember that the rent is pretax)
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For an EV, yes - the tax savings are better the longer the lease, whereas historically for an ICE car that wasn't FBT exempt, you would do a short lease instead for most value.