How about the iMac 20 Inch G5@2.1 Ghz? Do most of the features/items work on it? I assume it can drive a monitor like the Powerbook?
Is that silent? 2.1 Ghz puts it faster than the 1.67 G4 and 20 Inches might be bearable?
iMac G5 is silent only with low CPU usage. Maybe if you change internal fans for modern ones..
Also iMac probably slower than X5000. Here
is old comparison with MOS 3.15 ( Czech language ), iMac is often slower than X1000, and X5000 is faster than X1000 in most cases. And numbers in article for X1000 is with AmigaOS - MorphOS is more effective on same hw.
If you look here on hardware
, you can mentioned that your criteria meets only few, if any computers.
1. Quiet running: only low-power machines, or X5000 if you properly set fan speed. Other possibility is change Powermac G4 or G5 for modern water cooling - it will be silent, if you do it right.
2. Best performance: Powermacs or maybe X5000 ( I have no one, so I cannot say ). Performance of mentioned Powerbook also not top.
3. Dual monitor: Powermacs, maybe X5000. For sure not Pegasos
So you should test X5000 if fast enough and dual monitor capable, or make new water cooling in Powermac, or cancel some of your criteria
Maybe also one wide 54" monitor serves you similar way as dual monitors - I am not know your usecases.
AmigaOS3: Amiga 1200
AmigaOS4: Micro A1-C, AmigaOne XE, Pegasos II, Sam440ep, Sam440ep-flex, AmigaOneX1000
MorphOS: Efika 5200b, Pegasos I, Pegasos II, Powerbook G4, Mac Mini, iMac G5, Powermac G5 Quad