Thanks, there I have it.
I had hoped Apple had a better solution, and maybe I was overlooking, but I guess the incremental is what I have.
There's recommendations to do automatic full backups after several incremental, and with 3tbs, its not reasonable on my 2007 iMac. It would just bog it down while I'm trying to do multiple things on it already. I'm thinking that I'll just go back to manually do it every few months like I did with my old 750gb drives I had before, and anything of serious value, I'll manually add to backup in interim. I mean, its mostly podcasts and things like that, which need to be replaced on the backup drive, and that won't take as long as backing up the whole drive every so often.
Maybe there's a hybrid version of incremental and manual, but it starts to get into headache territory, so I hope I'm making the right decision. If Mac offered the dual folder drives, that would have been awesome.
Not sure if usb 3 on the drives help, don't think my Mac processes usb 3 speed. The moral of the story is probably to upgrade my system. But it just works so beautifully for everything else I do now, so it seems a bit much to upgrade a system just to make my backups easier. I guess time will tell.