I can format FAT32 up to 200 gigs with Partition Magic, but I want to use all of my 250 gigs obviously. When I got the drives they were formatted for FAT32 using all the space of each drive(250 gigs X 4 drives).
Also, I've been getting a "delayed write failed" error and never got it when i had the drives as FAT32, could be ironic, but i've read elsewhere that others have this problem with externals and ntfs...
Theoritically speaking FAT32 can support up to 2^32 sectors, IOW 2TB if each sector is 512bytes and the max file size is 4GB. Depending on the program you use to format the partition it can limit the maximum size of the partition (like XP limits to 32GB). I haven't used Partition Magic for a long time so I'm not so sure, have u tried format the partition into extended partition yet (as you don't use those drive for OS anyway)? Or format from your Mac (I don't have one so I don't know). I think you can also ask Norton, PM's author, for help.
About those ntfs writers for *nix I've only used them on Linux: NTFS-3G with FUSE runs about one third the speed of windows (as it's a library that runs in user mode), the kernel driver can only read (for now) but as fast as windows' one.
PS: About cluster size, the bigger it is the more space will be wasted (as a 1byte file also takes up one cluster). But if your files are mostly large file then it doesn't matter much.