If you decide to switch over to an M3/M4, you should know that depreciation varies based on the spec of the car. A G80 xDrive, as long as it's decently optioned, i.e., equipped with laser lights, carbon buckets, 360 cameras, and the executive package, will hold its value the strongest. The convertible, as is the trend with all M models, will have the weakest value retention.
To give a real-world data point of how well the G80 holds value, there's this one listed with almost 60k miles, and the dealership is asking $68,995. It's currently the cheapest priced *clean title* xDrive sedan, so I don't think they'll struggle selling it. Assuming the car's trade-in value was in the low 60s, driving a car 58,000 miles and only losing 25% or so in depreciation is incredible for a BMW.
https://www.pacificautocenter.com/ve...33ay07nfl82703