5.9
No idea (haven't booted into OSX on it for ages)
"If you don't take a temperture, you won't get a fever ..."

On the PB5.9 the drive sits beneath the trackpad. There's only a temperature-sensor for the trackpad, not for the drive itself.
Compared the the 12"PB with the drive sitting beneath the left palmrest, the 15"PB doesn't feel warm at all both on the palmrest and on the lap since temperatur-radiation lies in midair between legs (only the bottom beneath CPU and GPU tends to get very warm).
E.g. on heavy load my PB5.9's temperatur-sensors may show 36° for the trackpad while the CPU is at 68°C and triggering the fan.
Temperature mesurement and fan-controll is completely different between the 12" and 15" powerbook, maybe because CPU, GPU and drive are crammed very close together in a smaller case. Finally no problem with G4FanControl on the 12"PB where on the 15"PB it's not mandatory.
That really makes me calm down about the Delock-Converter since otherwise its a good product working on all PPC books and my old AcerTravelmate without any problems. I wonder, if any other converter runs into the same temperature-problems on the 12"PB (which BTW has got CPU repasted and new thermal pads for the GPU)
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That would surprise me. The excess heat is really down to how well the adapter deals with the voltage stepping from 5v to 3.3v. Cheaper adapters rely on heat dissipation, which is not really Apple's forte, imho.
I had a Kingston SSD that thought nothing of idling at 65°C whilst the Sandisk in my iMac barely gets over 20°C unless I stress it. Most SSDs should run at comparable temps as spinners. They consume similar amounts of energy when working after all. Any energy savings should be down to access time. You would need to keep a spinner running longer to access any random piece of data compared with an SSD.
The question is, which adapter deals decently with the voltage-stepping.
I use the same mSATA+Converter combination on my 12"PB1.5GHz and my 15"PB1.67GHz.
The small book sports a temperature-sensor, the bigger does not.
Temperatur on the surface (handwrist/touchpad or bottomside) feels very warm on the 12"PB and normal on the 15"PB
Distance between GPU and drive is less than a centimeter on the 12"PB and more than 10cm on the 15"PB. The heatsink is even more far away from the disk close to the egde on the display side close to the fans and the backside and it's located at the bottom so heat coming from CPU/GPU stays quite on the opposite side of the drive.
I guess the heat problem is more a problem of the hot-parts of the 12" PB sitting next to the mSATA causing the difference. Both PBs behave similar in getting very warm at the bottom-side just beneath CPU and GPU and maybe the metal-frame of the Delong-Converter also acts like an additional heatsink for the GPU.
My first SSD for PPC was an OWC-Mercury-IDE-SSD for my 12" iBook which also gets remarkable hot at the bottom despite of the plastic-shell which does not conduct heat as good as aluminium. I mean, at least that drive ought to have a decent voltage-management.
About energy-savings: can I make the disk go to idle-mode by any means before the Mac goes to sleeping mode?
12" PowerBook (HeatSink running "vertically" from drive to backside one edge very close to drive)
https://d3nevzfk7ii3be.cloudfront.net/igi/g3MBQxTXaWgpVHLC.medium
15" Powerbook (HeatSink running "horizontally" from side to side on the backside far away from the drive)
https://d3nevzfk7ii3be.cloudfront.net/igi/LXVWFPPwUMniWJCa.medium
(while I'm writing this my 15" Powerbook's Trackpad-sensor keeps on showing 37°C - so no problem about too much heat from the mSATA+Converter at all)