"In the long run" means you will have a team, you can rewrite the whole
framework to optimize things then.
[IMHO] It depends more on what you can do with PHP or rails. Can you write
clean code in PHP. Do you understand the rails-code (the framework-code,
in parts)? Can you fix or rewrite/enhance something when it really gets
ugly and nobody seems to have this same problem, so you _have_ to solve it
by yourself.