XMLReader vs. SAX

i have some general question about XML Processing in PHP5 with "event based"
parsers like SAX and XMLReader:

- first, is XMLReader more "lightweight" than SAX meaning less powerfull? in
fact it is simpler.

- is XMLReader faster than SAX, especially if you want to create a DOM
structure with SAX-callbackfuncs or with XMLReader->expand()?

- isn't it possible to programm an "xmlreader" with SAX? would this be
better/faster than XMLReader extension? SAX: can you stop the processing
procedure while xml parsing?

So, please enlighten me:)

Thanks in advance,
vivian