Since I do not know your CMS requirements, I will not be able to comment on the selection of CMS. However I will be interested to know how you finalized on Lenya CMS and Documentum CMS. Lenya is XML publishing based Web Content Management and Documentum is a traditional Document Management System.
Apache Lenya is a XML publishing engine. Both Cocoon and Lenya have a long history (since 2000). Though Lenya has good features, somehow customers did not embrace it as compared to other CMS.
On the other hand Alfresco provides wide range of solutions including Web CMS, Document Management System, Records Management and Collaboration. Alfresco has enterprise features such as clustered hot deployment, high availability, highly scalable repository and the world's fastest JCR repository.
It is not going to be apples to apples comparison between Lenya and Apache. Based on your requirements one of them might be more suitable ....
We as a services company take up such strategic projects helping customers choose the right technology.
My advise is to look at CMS as a strategic initiative and not to go with sites like http://www.cmsmatrix.org/ and do feature comparision.