[Zope] Zope vs. the Big Boys

Honestly, how does Zope compare to some of the big names such as BEA and WebSphere? My company is looking at spending a lot of money in the Application Server realm, and I wondered how Zope stacks up against them. We're two shakes of a pen away from purchasing something, and I'd like to at least come back with an open-source solution just so that we can compare something. Fire away. I need as much ammo as I can get (although, honestly, I'm leaning towards BEA) R