LOL, I told you this in e-mail. Don't trust me?
The 4400, 4200, 4500, 15000 do not have a HD limit I am aware of. There is a 21TB limit for the file system, but since there are no 5 TB drives out there I am aware of either, then this effectively means no limit.
There are 1TB drives now, but none in PATA (EIDE) that I have seen yet, so this means 750 GB drives. I know the above listed units will support 4 x 750 GB drives (been there, done that), at least with Guardian OS 4.2.054 and above (never tried it with an older OS, so can't say for sure on them).
Now you have heard it from me twice...