Just tweaking the system is all you can do. The trick to tweaking a system is to take as much load off the hard drive as possible.
Memory can transfer data at GB's per sec. The CPU can handle even more. But the hard drive goes between 50 to 100 MB's per sec. That is a huge bottle neck. New SSD drives are getting faster (Up to 350 MB's so far) yet still way behind.
So on a lot of systems the slow down is waiting for the hard drive to finish reading the data the system needs. So the more tweaks you do that take away anything needing to read off the hard drive the more the hard drive has speed for other things
So like my simple system tweaker. It has only the safest tweaks I found and they work. Every service you turn off is one less file that the drive needs to read and one less program running that will access the drive. So the less things running the better.
Shane