Pegasos 2 today is nearly 15years old. It was great machine and still is not bad today. Only for web-browsing and video we need more power.
I overclocked Peg2 to 1.33MHz, equip with Radeon9800Pro and now test some HDD and SSDs:
( test was made with SATA300 HDD and SATA300 SSD )

Possibilities to connect HDD/SSD:
1. onboard IDE/PATA controller with SATA reduction
theoretical params: UltraATA 100, mode 5, transfer rate 100MByte/s

2. onboard FireWire400 controller
theoretical params: transfer rate 400Mbits/s = 50MByte/s
- usable only for backup HDD/SSD, or for connection of USB2.0 hub to save PCI slot

3. PCI card SII 3x1x - SATA I
theoretical params: transfer rate 150MByte/s SII3x1x, 133MByte/s PCI slot

4. PCI card Promise - SATA II
theoretical params: transfer rate 300MByte/s Promise TX4, 133MByte/s PCI slot

Here is graph from SCSISpeed Results:
srovnani-jpg

Best results - read speed, MB/s:
PCI card Promise - SATA II 114 MB/s
PCI card SII 3x1x - SATA I 84 MB/s
onboard IDE/PATA controller 55 MB/s
(FireWire not tested, too slow)

Unfortunatelly, Promise - SATA II card is not supported hardware and you must use third-party driver ulsata2.device. It mean, that you cannot boot MorphOS System: from Promise card, and it limit it's use only for Work: and Backup: volumes.

Why PCI card SII 3x1x - SATA I so slow? Theoretical limit shows that show stopper is PCI (133MByte/s), not SATAI (150MByte/s), and PCI is the same for SII and Promise, but:

Let's compare software drivers: (info from morphos-debug.log and SysMon)

MOS 3.11:
onboard IDE/PATA controller ide.device UDMA5=100MB/s S.M.A.R.T no
PCI card SII 3x1x - SATA I sata.device UDMA5=100MB/s S.M.A.R.T no
PCI card Promise - SATA II ulsata2.device UDMA6=133MB/s S.M.A.R.T yes

AOS 4.1FE:
onboard IDE/PATA controller peg2ide.device UDMA5=100MB/s S.M.A.R.T no
PCI card SII 3x1x - SATA I sii3114ide.device UDMA6=133MB/s S.M.A.R.T yes
PCI card Promise - SATA II no driver at all

It looks that sata.device is not ideal - recognize SATA HDDs only like UDMA5 devices, and have no S.M.A.R.T. feature. It is not hardware issue - AmigaOS recognized it correctly.

And what to do now? It leave us on Pegasos2 only this possibilities:
- System: (and complete AmigaOS) on IDE (55MB/s), other MorphOS/linux volumes on Promise(114MB/s)
- all volumes on SII (84MB/s)
- System: (and complete AmigaOS) on SII (84MB/s), other MorphOS/linux volumes on Promise(114MB/s). But it takes two of three PCI slots.

I don't know the priorities for next MorphOS, but improve of sata.device will be great, at least for Pegasos owners.