I'm using 20gb 7200rpm IDE HDD's, I got a job lot of NOS Seagate drives and use them with SCSI-IDE converters in my big box Amiga's, I get up to 10mb/sec on my SCSI-2 devices. Of course you can use larger drives.
I use SFS and as they are on SCSI I do not need IDEFix, etc as the 4gb limit does not apply on SCSI.
My Yamaha SCSI-IDE adapters cost about £30 each and I have three of them now. Well worth it IMHO.
