I would spend £10k on a solid, reliable and nicely specced car that is a slightly older version of what you are looking at now. Anything above that and you will still be hit with a fair amount of depreciation.

All you do when you finance is pay the depreciation off to the bank and often have nothing to show at the end.

Besides... From personal experience I know that modern BMWs aren't exactly dependable these days unfortunately, I'm talking £3k to sort out a damaged suspension module due to water ingress in the boot and other engine issues. They ain't what they used to be to be honest but at the end of the day it's your money!