To which framework should I migrate my app?

I started a new job wherein I was tasked with taking on a large codebase that was developed by means of outsourcing. However the codebase is riddled with problems, not least of which is that they have never updated the web framework - it currently is built upon cakephp 1.3.x.

It turns out, that:

1. Upgrading this framework is an almost impossible task.


2. I cannot host this app along other apps on apache without reconfiguring my server to use fastcgi/fpm, and installing unmaintained versions of PHP.


3. I am barred from using plugins that expedite some elements of the development process.


4. There may exist security vulnerabilities from using outdated versions of PHP for a product.

-- among many others. To address this I decided to build a business case for rewriting the app using a different framework. Of course, in order to be a viable solution I need to be able to ensure that:

5. 
   

   Rewriting the app will not take up as much time as developing the app was in the first place.

   
   


6. 
   

   It works!

   
   

For these reasons I was hoping to use Ruby on Rails as a fast prototyping framework for this task. This is as far as recommendations to myself go. Considering the points above, could anyone give me a thorough reason why I should rather migrate to web framework X?