From the few benchmarks that I have run, Squeak looks very promising.
However, it is very difficult to tell what Squeak is, due to the lack of documentation.
Squeak by example is more than 6 years old, and only by a stretch of the imagination may it be called a user's guide.
It certainly is not a reference manual. Other documentation seems very dated.
Commercial products ( such as VisualWorks ) provide a lot of documentation, at a price (or free if you use their non commercial version). Maybe Squeak has comparable functionality to VisualWorks, but it is difficult to tell.
It seems to me that development has far outrun the documentation and only the developers know the true capabilities of the product.