I've found that the really important bit when writing read-heavy web-apps is good caching. The write-path could be written in something slow-ish and it will be hit far less than the front-caches serving data.
So, if you need a web templating language + basic json callbacks, php will definitely do the trick for version 1.0 (or ruby-on-rails or whatever gets you up to 100% feature complete). I've written game backends which did ~2.5k-3k rps on a single machine with PHP (though, I did have to fix PHP APC's locks to handle those loads in the process).
But then you still need to know JS to write the frontend code.
Node.js basically lets you combine 2 skill sets into one - the frontend and backend can share the same data model code for instance. This is easy if you have complex data-structures to communicate between the two layers.
Go actually gives up that advantage, but wins out because it can do compute intensive tasks faster - and can do state-ful daemons in a much nicer way. If you were building say, an online game, where say it was poker game with low-latencies, I would go for go. Definitely.
But as it stands, the only reason to go for Node.js is that your front-end dev can double as a backend-dev. Otherwise, I'd stick with what you know & are most productive in.