Report: Mac Mini G4 1.25GHz.
I replaced the internal 5400 RPM 40 GB PATA HDD with an mSATA 128 GB card + mSATA-to-IDE case.
Swap went flawless, based on youtube video how to disassemble the mini to reach HDD. The mSATA-to-IDE case have identical dimensions of the original 2,5" HDD, so the swap was easy. There was no jumpers on the old drive and no jumpers applied to the new drive, it just works as it is.
The result is shocking under osx 10.4 xbench disk speed test. Total of 210 xbench points of the mSATA drive.
4k reads (not random) are up to 99 MB/s, this means it is saturating the IDE bus which has hardware limit of 100 MB/s (Ultra ATA/100 standard). It is not just the synthetic test that feels fast, it have the usual feel when you swap HDD with SSD.
Basically the Kingfast mSATA card considered shit in the SSD world due to small file random read/write performance, still it is smoking any IDE-HDD in access time. It is also cheap!
Also, when you got bored of the mac mini, you can reuse the mSATA card, there are external USB 3.0 or USB-c mSATA cases, so you can convert the mSATA card to a nice, small sized external drive.