i like to second redrumloa's first point here: If you want to keep OS4 on X5000. better just keep it as it is and get a dedicated machine for MorphOS. My suggestion: Powerbook 5.8/5.6 or an iMac G5 20" isight. These devices are cheap and play in about the same performance league as the X5000 and are fully supported by MorphOS. And best is: You can run MorphOS and OS4 simultaneously.

Cost of an iMac g5 is not much higher than a gfx card you'll need anyway. Add a few bucks for a new ssd, and you're done (IIRC I paid 80 for teh iMac and about 30 for a Kingston SSD).

Only disadvantage I see is the additional required space on/under the desk, but on the other hand you'll win some redundancy which - in my experience - is quite a good thing.