I'm also developing in Rust, with a 12th gen i7-1270P. It's an absolute beast; I'd say it's on the range of 2x speedup vs my previous laptop (11th gen i7).

I have no idea about power consumption yet (the laptop is a couple weeks old). On light load, the laptop easily crosses the 8h mark but it won't, certainly, when grinding rust compiles. The M1's power efficiency is on a different league.