@fhall,
are you using one or two of these adapters? I recognized, that when you use two of these green adapters or in conncetion with another IDE-HDD in a PowerMac G4 Sawtooth on the same IDE-ribboncable (Master and Slave) it takes hours to boot and then it will not access without trouble (like transfer rates of 3MB/s and stuttering access). But used alone they seem to be ok. I have one with a red board and Marvell Manhattan chipset, that also has a jumper for Master and Slave.
On the IDE-SSD buying thing, one might want to compare first, if an IDE-SATA-adapter plus SATA-SSD is not cheaper than an IDE-SSD, also considering that you have enough room and can use a 3,5" SSD, which (both the SSD and the adapter) are cheaper than the 2,5" or mSATA variants. Also, IDE-SSD boards are made differently. I can't explain really, now, but it seems that SATA-SSDs do have the better tech. That is, if you find an SATA-SSD that is SATA-II or an SATA-III SSD that is compatible (results vary form user to user).