We are about to embark on a large enterprise application. I am seriously considering using ASP.NET MVC because:
No. One thing that the ASP.NET MVC has over ASP.NET Web Forms in terms of performance is that it doesn't make use of a control tree. The control tree consumes a lot of server side memory and keeps the garbage collector very busy on pages with many controls. I would argue that you would get superior performance from the ASP.NET MVC. The unit testing aspects of it are a real win to.
The flip side of this is that you can't use all of the handy out of the box controls that you get with ASP.NET Web Forms and you'll probably end up doing more client side JavaScript development so the initial development budget would probably need to be greater if you choose ASP.NET MVC over Web Forms, but you would have a superior solution for the long term.