Did you know that you can run Squish GUI tests in parallel using Squish's new TeamCity plug-in?
See our froglogic blog entry or read more below:

Using Xvfb to establish additional virtual display servers, you can configure your TeamCity project to contain multiple build configurations, each of which can run your Squish tests in parallel.

Learn how here: Running GUI tests in parallel on a single host

Read more about Squish’s TeamCity Integration here