We plan TeamCity 8.0 release for for this (or at most the next) week and here is the last chance to try pre-release version on your server and let us know if it plays nicely in your environment.
The build is of release candidate quality so give it a try today!
Here is a list of fixed issues and one of them is pretty interesting: TW-16735 Allow to use more than 20 build configurations for less than full TeamCity Enterprise price.
And that one is actually implemented in 8.0!
Weighting several options we decided to go with the one to make each build agent license also add 10 build configurations in addition to one agent. This obviously applies only to Professional edition. All the agent licenses valid with TeamCity 8.0 will add 10 build configurations each once you upgrade.
Hope you will find this useful as well as other 8.0 features.