I can't offer any specifics but I suspect that some inappropriate settings are causing the slowdown.
In Safari you could try to empty the cache or even do a reset and see if that helps.
Last summer I had a system that was performing like that. Launching took a long time, web pages opened slowly.
I wiped the hard drive and reinstalled OS X from scratch. After that system performance was great. Same OS, same applications.
There could be a simpler way to do this, if one knew what to do.