an article comparing wicket and jsf+seam
The blog post compares the performance and memory footprint of Wicket vs JSF+Seam by implementing one of seam examples in Wicket.
Bottom line: Wicket is a clear winner.
The author has other implementations, including for tapestry, grails and wicket with groovy / scala: http://code.google.com/p/perfbench/ (anyone up to writing a django implementation?)
Regarding Scala vs. Java, here's the same wicket page in Scala and Java: