As far as performance, the Alto team described the performance of Smalltalk as between "majestic" and "glacial". From my experience with the Alto, Smalltalk seemed unusably slow, and I'm amazed that they could actually accomplish anything with it.
With the ParcPlace flavour teamwork with Envy version control was pretty slick. And in performance it was mostly compiled to bytecode with some cunning tricks in place to make interactive debugging appear to work at the source level. Truly great environment for exploratory development: concrete example, while building a comms server I could inspect why message handling failed, patch code, rerun from failure, much faster cycle time than most other langs/envs.
The Xerox Dorado, an ECL beast evolved from the Alto, was considered the only machine to offer a good Smalltalk experience when Smalltalk-80 was initially released. The Xerox Dolphin, for example, was only about "0.1 Dorados" despite being a serious improvement on the Alto. The Apple Lisa was only about 0.05 Dorados.
That level of performance was only achieved by PCs when we got 50MHz 486 (for purely interpreted Smalltalk-80 virtual machines, with JITs much slower computers could match the Dorado).
