The first iteration of Rosetta that you've mentioned exhibited lower performance (often a drop of over 50%) compared to software run natively without any translation.

While regular applications may run on Apple's new lineup of Mac devices, we'll have to wait and see whether Apple lives up to its promise. Rosetta 2 is definitely a step up from its predecessor but I'd still wait for reviewers to benchmark these new chips.

Here's an in-depth article with benchmarks on the transition from PowerPC to Intel's chips: https://www.macworld.com/article/1048991/imaclabtest1.html?page=2