> How can it be too slow on modern hardware?

It can be, because it is :) If you want a really technical explanation, you can profile the application. If that is too much work, I'll generalise and say that the tendency for the UI to lock when performing CPU heavy computations makes it feel slow. Because of the things you will be asking it to do (i.e. solve modern problems), sometimes such computations exist and lead to blocks of 1s or more. That will never feel fast.