How are your loading times of the User Profile Service Application pages in the Central Administration ? Mine are often beyond one or two minutes, for example when adding a new user property. I am not sure where to look. I have defined only one synchronization connection to our Active Directory server and the profiles import works ok, so I am not sure this is the problem.
Typically the performance I've seen is pretty good with 3-4 second load times. I would start by checking the overall utilization of the servers. If for example this is the sole application server and it is also running all of the other service applications then that may be an issue. With this in mind, there may be additional delays during a full crawl.