It appears to me that, except for the 5V startup, the 9GB drives require _less_ power than the 4GB drives. Is the 5V startup the limiting factor? Can the power supply not deliver 1.2 amps at 5V to six drives? Is startup power the power required to "spin up" the disks? In that case, isn't that power only delivered once at boot time? Do the disks ever spin down in an active system?
I can't explain why the stated power requirements seem to be compatible; I only know what was learned with actual experience and testing. The spin-up shouldn't be an issue since, as someone else pointed out, filers spin the disks up more or less sequentially. But in any case, when the 9GB drives are active, the draw on the power will pull the write line of the drives down to unacceptable levels. This didn't happen with the 4GB drives.
I really don't mean to be confrontational. We're just desperate to get some more life out of our F210 (we bought it new just two years ago).
When you bought it 2 years ago, due dilligence told you it would not expand beyond a certain size without investing in a new system, right? You chose to save money then and pay for it later. Well, now it's later.
About the only other advice I could offer is if you're going to try to use the drives, make sure you are doing regular backups and only use like 4 drives per shelf. Have additional 9GB drives available as spares since the failure rate will probably be higher. This will get you like 30% more storage on your F210 than you have now.
Bruce