There is more things to do that can help improve designer:
1. Designer use a 32 Bit Java machine and is preconfigured to use 1 GB of RAM max, but it can Use at least 1536 MB , in the designer folder you will find a file called: Designer.ini with the java memory configuration, user this setting:
The java in desginer 4.0.1 can't use more than this memory.
If you are using Roles and Entitlements, belive me this extra memory will help you
2. If you have more than 1 proyect, remember always disable the proyects you dont use:
Project TAB -> (Right clic on the project) Disable Project
3. Remember the more tabs you have opened, the more resources need for Designer, I found that there is a tab called: Provisioning, that try to maintains a lot of things in memory, if you don´t use close it, and restart designer, try to use insted (if you can) the Tab called OUTLINE.
4. If you have more than a server per driverset, always set a preferred server:
Right click on the Driver Set -> Server List -> Preferred Server, and set the one you chose, this will improve and will correct an issue on drivers creation that consist in the following: When the project is too large and you create a driver, the driver does not store the configuration you gave it through the proces, all the XML configurations stay in blank.
I hope this help