Problem is that IDE --> SCSI bridges cost an arm and a leg, figuratively speaking ... well, not really, they are freaking expensive
... If I were to buy one of those for any of my other Macs I would probably go all the way and throw in a CF adapter and CF card, then call it good.
You have to consider that pretty much ANY recent CF card can easily saturate the SCSI II bus in terms of transfer speed, not to mention it's a "solid state" solution, no noise (granted, I love the "clickety" sound old hard drives emit), low power consumption, and last but not least, your data would easily be readable through any CF capable card reader.
In addition, a solid state solution is not going to suffer from performance issues due to e.g. fragmentation or drive geometry like a regular hard disk would. Since there are no physical sectors or tracks which have to be accessed, rotational delay isn't an issue. Access times are generally much faster than any hard drive and generally won't vary much like it would with a physical drive (seek time etc.). Before I switched to CF I used a quite decent Toshiba hard drive in my PowerMac 6500. Benchmark results with my CF adapter show a great increase in overall throughput and performance in comparison to the old drive.
-- BeniD82
P.S.: I use a CF solution for both my PowerMac 6500 and 640 Dos Compatible, works like a charm!