The main point is that output of
String objects with a Writer involves character by character conversion from UNICODE to the output format. A plain OutputStream just sends bytes without examining them. Bulka's book "Java Performance and Scalability Vol I" has some pretty impressive comparisons - of course that book is several years old by now.
Don't jump to the conclusion that any particular technique will improve your performance until you have actually verified where the bottlenecks are.
Bill