Peter Thomas has created a detailed performance analysis of Wicket, Tapestry, Grails and Seam. It's an interesting read from non-Tapestry user's perspective, and complements Ben Gidley's findings.
He's measuring raw performance and Wicket narrowly bests Tapestry in most categories, with Seam pretty close and Grails much further out.
I'm disturbed by some of his problems developing the application (with respect to adding client-side credit card number validation) and there's no mention of Tapestry's other qualities, such as live class reloading, exception reporting, etc. Still, criticism of Tapestry's documentation hits close to home (and it, alas, too fair). Accurate and very complete, but not organized for a beginner ... something I'm hoping to address over the next few months.