Zend Framework is a good framework but not very fast. Can you tell whether it\'s worth using Zend Framework for highload projects, for example, for email marketing service t
Seconding Joe's answer. I've also seen ZF deployed on a few sites handling millions of requests and have yet to encounter a problem. When dealing with that amount of traffic it's a good idea to use other strategies beyond your framework, including but not limited to caching and the use of a CDN.
I've found most frameworks will call or create many class instances per request which I think is what causes people to say that framework X is slow without having any real world experience with it. Any hit you take there can be easily mitigated by using an accelerator and caching.
If you already have a team of devs you've hired, I'd suggest using what they feel most comfortable with and have the most experience with. Best case they'll be able to tune their code for that framework.