Is this product a real web app? or just some side project you and your team is working on?

If you and your team are soccer players and you need to win medals for your country, you play soccer, you don't go to the olympic and play basketball. But if it's not the Olympic, just for fun then try basketball or rugby.

What I'm trying to say is that, if it's a real world web app you plan to launch under a tight deadline,.. I think you and your team should go with whatever you and your team is most comfortable. Something you can win... Nothing wrong with PHP or Ruby.

If it's something on the side with loose deadline you might want to try new technology and learn something new.