I do not know what your criteria of "not slow" is. I find mine starting to get a bit slow when I get about 6-8 applications open, depending on what kind of application of course. The only exception is the browser which I admit is a bit sluggish, but there is not much you can do about that.

To install the most up-to-date firmware, follow the "Maemo community update" link at the top right.
You cannot miss it, it is a big icon like this:



You will have a number of choices there. I personally use CSSU Thumb and can wholeheartedly recommend it.