I have to agree with both of the users above, the UCA console is not intended for a high volume traffic, think less than 50 calls per hours maximum... although the couple site we have running it successfully are very small (less than 50-100 phones) and more in the 15 calls per hour range. In larger environments it is kludgey to use. AND every UCA update seems to fix something, and break something.
Basically, if you have a site with a dedicated operatoror or any operator that handles 50+ calls per hour, stay with the 5550 console.
The one real advantage to the UCA console is the IM capability, it is very useful, but higher traffic areas can't really make use of it as the operators don't have to time to use the feature effectively.