Dark-morph Buteos: how to ID (1 Viewer)

Hello everybody,
what are the most conspicuous features to search for when trying to identify a dark-morph Buteo sp.?

A bird like this has been recently spotted in my area (NE Italy) and some talk over its id resulted in:
1. Long-legged Buzzard (Buteo rufinus, ssp. cirtensis?)
2. Steppe Buzzard (Buteo buteo, ssp. vulpinus?)

Is Buteo buteo ssp. buteo a possible alternative? Are dark-morph individuals of this ssp. as common as the other two?

Thank you for any food for thought you may provide

Regards,
Max

Buteo morph project

Buteo morphs are difficult, and that's why there is prejects like Buteo morph project at the Max Planck Institute for Ornithology which allow people to contribute to this research topic.