Processor upgrade?

Flash is slow on any Mac.

Go to lowendmac.com, they have a lot of info about processor upgrades. Depending on your model, you may be able to upgrade to dual G4 processors.

Remember that the architecture of the computer isn't particularity fast, so a faster CPU will only go so much.

 

A 400MHz G4 could be either a Sawtooth
http://lowendmac.com/ppc/sawtooth-power-mac-g4-agp.html
or a "Yikes" (PCI Graphics)
http://lowendmac.com/ppc/yikes-power-mac-g4-pci.html

Most (but not all) Sawtooth G4s can be upgraded with dual processors.
https://eshop.macsales.com/tech_center/index.cfm?page=Static/uni-north.html
Yikes G4s can only be upgraded with a single G4 (or a fast G3) ZIF.
On the Yikes, G4 CPUs of 700MHz or higher will slow down the bus speed (throughput) by 1/3, to 66MHz, down from the original 100MHz bus speed. This is a workaround for a hardware compatibility problem with later G4 chip revisions. Faster G3s can use the Yikes' full bus speed.