This is a G4 iMac. If it's 800mhz or above it will run 10.5.8 natively. There are other methods to get 10.5 on to these systems, XPostFacto being one of those.It's got OS X 10.5.8, which is not supported by Apple in this iMac of mine. Can't even remember how it got there, must have been XPostFacto or something similar. But that's probably the most you can put in to it, wouldn't you think?
There are two stickied threads at the top of this forum that tweak T4Fx for better speed. One of the extensions to install that will help is either uMatrix or NoScript. Most of the slowness is due to javascript garbage. Block that and things speed up.Ok, now I got in. Seems to work ok. Pretty slow though.
MacRumors uses Javascript and when you have the WYSIWIG editor for posts active then JS is active. Turn it off and learn to use tags for bold, italics, etc and MR will run faster.