I don't know for sure about the GVP HD+ controller, but it looks like it's the same as the GVP HD8+ controller according to BBoAH. At least I have a 2.1 GB harddrive installed, full capacity in use over 4 partitions, with the largest partition being around 1 GB. I have an external CD drive connected as well. All fully working on Kickstart 1.3.
I once tried to get a 4 GB harddrive up and running in the controller, but never managed to, and haven't attempted ever since.
