I just did those calculations, comparing a leased 737-900ER BGW to a bought on (with full sum as a loan). This is what I end up with at 0.8% interest:
Interest payment: 12.6 million AS$
Leasing payment over the same period (50 weeks): 15.5 million.
Note that a leased plane isn’t your property yet after that time, whereas your bought plane will be. Also, you can pay back the loans at any time (cutting down on interest payment), while you’ll always be stuck with your leasing rate (which doesn’t adjust for age as long as your contract remains active, as far as I know). You could, of course, invest in the plane by buying it, but it’s only really profitable to do this before the 39th week (at least, at 0.8% interest. The lower the interest, the sooner you hit break-even), since after that, the interest payments from the loan bought plane would be lower than the leasing rate (meaning you would have paid more leasing than you would have for interest).
That being the case, the general conclusion is probably still that leasing is the way to go, unless you have mountains of money that you don’t know what to do with. Also, you could consider taking the loans anyway and just lease more aircraft instead of buying a single plane. It’d get you more profit that you can then use to pay back the loans (or invest in even more aircraft).
In the end, leasing will always be the better option, because of both its flexibility and its lower strain on your finances.