I know I'm biased but numbers aside, I can't think of a single meaningful way that the BMW is better. The LC is much better looking, better sounding, will be more reliable, and the LC will hold its value much better. If you're talking about the M850i rather than the full fat M8, that thing depreciates so fast you'll get a nosebleed. 3 years old, 13k miles, and a ~50%/£50k haircut. I reckon it's a long way from being done setting fire to your money if you buy it, 2-3 years it'll probably be £30k. Sod that!
I guess the BMW might be better if you want straight line bragging rights and the "right" badge to impress people in a pub. Haven't driven one but plenty of reviews have said that from inside even the proper M8 is just like any other BMW, and from the outside it looks like a flattened 4 series.
At these prices you're buying with your heart rather than your head of course, whether you buy the LC or the BMW, and the BMW just doesn't seem special enough to me. The LC obviously did 😁 If the BMW appeals to your heart then go for it.