EJB or web service

We have to make a component available to three applications. All the
applications and services have to be deployed on the same clustered
server. Now I know EJB is one of the options available to us and it
will work well.
However I am very much interested to make it a web service. Now I have
following questions -
1. Will the web service be slower than EJB. If yes then why?
2. Is there any way to speed up the web service, if it is on the same
clustered server as its clients?
3. Do i have any other option except web service? Few persons suggested
to use XML (over http)?

Suggestions please

Thanks