If you're not doing a computationally expensive startup, speed won't matter much. If you ever get to the size where it does (i.e. Facebook) - there are always solutions.
I've been seriously considering trying to start up an alternative language that takes the best parts out of PHP, but drops all the backwards compatible nonsense. It really has some great features but the annoyances will scare off most top developers - and you're left with a crowd of 85% script kiddies and only 15% developers that actually learnt to use the language properly... and trying to find one of those 15% isnt easy.