I have 6.0.6 on my G5 and it's rock solid. I believe ProKit 6.x is for Snow Leopard only, so it shouldn't be an issue here.
My software:
Pro Maintenance Tools - Tools to keep Final Cut Studio, Final Cut Pro X, Avid Media Composer and Adobe Premiere Pro running smoothly and fix problems when they arise
Pro Media Tools - Edit QuickTime chapters and metadata, detect gamma shifts, edit markers, watch renders and more
More tools...