a few comments and questions:
1) yes, you can support up to 3 radius servers on a 2650...
2) in your 'show run' i did not see a command that allows the switch to send the 802.1x auth functions to the radius servers...it may have been simply edited out when you did the edits...
it should be something like this:
'aaa authentication port-access eap-radius'
3) i assume in each of the freeradius server configs (Clients.conf) you have defined the 2650 as a radius client with the same shared secret...
4) on radius server x.z, if you looked at the /var/log/radius/radius.log did you see requests coming from the 2650?
5) finally, if you remove the x.y radius server config in the 2650, does it work?
'no radius-server host 172.16.x.y mykey'
hth...jeff