Picking The Right Web Technology?

I need to create a web application where the layout of the site is entirely programmatically generated - about the only thing that's done declaratively in the markup is the header. Basically, it's one of those AJAX-enabled entire-site-within-a-single-page type of sites where huge chunks of content (structured as modules such as navigation panes for example) are swapped in and out on the fly. From lowest-level to highest-leveled, the options I've considered are:

Classic ASP - Since ASP provides full control over the final output, this would be perfect if not for the lack of separation between logic and presentation and the subsequent lack of code reusability. ASP.NET MVC - REST and MVC routing seem like a poor fit, since there's only 1 actual webpage. Also, interpreting and transforming data and even the UI itself based on business rules (as opposed to direct user input) lies well outside of the deterministic CRUD operations that MVC excels at.

ASP.NET Webforms - Tried something like this using Webforms in the past, but ended up fighting with the ViewState and Postback event model every step of the way. Needless to say, performance was extremely poor and the codebehind was a mess due to the complex logic needed to fully and precisely regenerate each and every single aspect of the page on every single Postback. Silverlight - To be honest, I've never used this. Non-Microsoft technologies - None of the popular ones (PHP, JSP/J2EE, Flash) are entirely suitable either.