Below are some possible reasons why your administration panel may be slow:
1) Version 4 uses more advanced technology. Like most new software it tends to take more system resources on the administration panel. This is not related to the speed on the system / server (the actual processing of data is much faster than the older versions), it's related to the speed and power of the computer it is viewed on.
2) Different Internet Service Providers (ISP's) use different routing procedures which may effect the speed minimally between the server and the panel. This is not related to the distance from the server but on the processes of the ISP's on the pipe your data is travelling along.
3) Some virus checking / firewall programmes take longer than others to allow data to pass through (for example, some new virus checking systems may send information to another server on the cloud to check the site).
4) Within your pages itself, you may have included script that causes the system to slow down, especially if you don't have up to date software on your computer.
5) Finally check you have the most up to date software.
