Grail or Ruby on rails for an highly interactive event based web application?

With Java and Perl background, I have narrowed down the web framework choices to Grail or RoR.

The web application is a highly interactive content management app ran on private cloud.

One vision is to make all the widgets on the web pages to be event driven: click, double click, right click, keyboard shortcuts, etc. Does either framework supports this?

I have developed with groovy on grails and ruby on rails. You can do highly interactive AJAX work with either of those frameworks - it won't matter which.

Scaling the application has more to do with caching, fronting the application with a high-speed web server for static content and that kind of thing.

When it comes to making a straight choice between grails and rails I'd consider two things:

• which of grails and rails are you most familiar with?
• do you have any legacy Java or Ruby code you need to integrate with?

Apart from those two considerations, there isn't much to choose between them.