I do feel I need a bit more power out of my system
I don't quite understand what you are saying, what do you mean by "power"

What you must appreciate is that you have some obsolete equipment there, and are pretty much limited to "going with what you've got"

A bit like Betamax and Philips 2000 video systems (anyone remember them )

You would need a Silicon Graphics "Multilink Adapter" (they don't make them anymore) then you could use more or less any graphics card that supports custom resolution and refresh rates.

This machine has an nVidia GeForce4 MX420 card (64Mb) which will do that. I am sure that there are many others.

Good luck