Screen dragging might be less useful today than it was 25 years ago, however is one of the unique features Amiga had, so I am really excited for the fact it has finally landed on native AROSland too.
Said so, I wouldn't expect AROS to run better than AmigaOS 3.1 on classic hardware: with some luck it will be not too much slower, but don't forget that 1) AROS won't have the "optimized in assembler" parts, for simple portability reasons, and 2) AROS is much more advanced, in many parts, to the OS that inspired it. More advanced means also new features that will require more porcessor grunt. In a nutshell, I think AROS on classic hardware will be something more than a curiosity, but the real uses for it will come from UAE installations and clones like the Natami or the Minimig, where there is more freedom about confugrations. Don't forget, too, that people using PPC accelerated cards will need to write software to handle them, or at least recompile the whole OS to take advantage of them.