This topic has been discussed a number of times (including recently) on this forum, check the archive. Certain lack of optimizations regarding resolving component names and evaluating ELs are a serious concern.
Personally, after several months of using Seam & JSF, I doubt it can be used for that level of performance (and I went to technical sessions about eBay's architecture and what performance problems they faced). Actually, I'd say that for that level of load, a framework's performance must be *proven*, not assumed. So far, I haven't used a really fast application built with Seam :-( I don't know much about this infrastructure of seamframework.org and how much effort has been put into it as a showcase of Seam, but many operations (search, clicking on [Knowledge Base=>http://seamframework.org/Documentation/KnowledgeBase]) take a few seconds.
Good luck. You may need it.
This topic has been discussed a number of times (including recently) on this forum, check the archive. Certain lack of optimizations regarding resolving component names and evaluating ELs are a serious concern.