Real test will be when we will be able to compare ARM vs x86 Macs. Here with emulator is too many unknowns.
Software emulator means x86 instruction interpreter, something like BASIC from ages ago and that's quite slow. Simply, even single byte x86 instruction will take multiple ARM instructions to do same job. Now imagine complex ones. Microsoft was not able to emulate x64 code on their ARM Surface. From article info it looks they just recompiled code but if they ran emulator then every other CPU company is finished. But I doubt it.
Do not forget Apple is doing everything to fool users. Watch Linus video about MacAir how Apple already started. Spoiler alert, let's make slow Mac on purpose and then release new one without limitations.