Well, compared to popular dynamic languages with similar levels of abstraction, like Python or Ruby. Squeak was just released with SistaV1, so I think the speculative inclining JIT is just around the corner. While using Pharo, I'm used to get code running 2-3 faster than the equivalent in Python.
The freely available book "Pharo by example" I found good to learn from, a few years ago. Smalltalk is an enormously powerful language but initially it can feel "the wrong way round" like driving on the other side in a foreign country . You can get used to that though, and its worth it. I think in the years since I learned Smalltalk via Pharo, its got a bit bloated with features, so Squeak might also be worth a look for trying out simple things to learn.
one of the most annoying things about smalltalk/pharo is that the "marketing" tell you it's simple and the syntax fit in a sheet of paper, yet all the times i tried to try it i had to go through a lot of pharo introductory tutorial before i could even start to type an "hello world".