I just can't justify buying hardware from a company that is so hostile to developers and hackers as nice as it may be.
You'd temporarily lose some hardware support (documented) while it's being worked on. But I'm not sure why you expect losing performance? This is running native code. Same binary will run the same on both systems (+/- the llvm version differences).
There are a bunch of factors that could affect performance even under the same OS (try underclocking your CPU or play around with schedulers). Given the mostly non-existent documentation from Apple I'd strongly suspect that average-case performance will stay worse on the Linux side for a long time.
Some of this stuff is handled by binary blobs that get installed/upgraded by MacOS, and are running by the time Linux boots.
With the previous release, power per watt and absolute performance were already better than high-end x86 laptops, so if your question is "is this faster and more power efficient than my other Linux laptop?", the answer is probably yes.
If you're asking if it will beat MacOS's perf/watt in all scenarios, the answer will be no for a long time. However, it is probably already beating MacOS in many practical scenarios.