I use some PMs here: 5x G5 from 1,8 to 2,3GHz and none is noisy! You can't nearly hear them.
If they are loud, it depends on some issues:

1. Correct calibration with ASD-Disk!
2. To set propper temperatures (setcpufancontrol) in MorphOS
3. Most of noise is'nt made by CPU-fans, but by backsidefan (radial-blower) which cools down North-Bridge! It is ablolutely necessary, that fan and heatsink of Northbridge is clean and thermal paste is'nt dry.
(Btw.: Changeing a defective radial-blower is a real challenge!)

There is something interessting too:

Older PM are able to work only with one CPU (you can dismount the second one) - open firmware recognize it.
In that case, Northbridge never get such high temperatures as when using 2 CPUs.
I found out, that such PM also can be used in Open Firmware console, without going into emercency-cooling after a while (and this is really loud).
PM can use up to 1,7GB RAM, different GraphicCards and other cards as SCSI, USB, Soundcards,.......as well.


Mini: Good system to beginn MorphOS. 32MB GRAM is'nt much (as said above), but enough for normal screen-resolutions like 1650x1080 (or less). Useing Wayfarer may be challenging because of only 1GB RAM.

PB: Have more power (1,67GHz) and more RAM (about 1730MB useable) ant they are mobile.

Pegsaos2: The allrounder - if you can get one: Capable to run MorphOS, OS4, Linux, MacOS (Emulation) and is expandable with cards.
Peg runs only with 1GHz, but it never feels slow. Peg can normaly use only 1GB RAM, except last built (Rev. 2B5), where stable working 2 GB are reported.


MorphOS is also running on ACube Sam460cr/cx and A-EON X5000.