mac 2.1

I have updated the firmware in my MP1,1 to 2,1 in prep to upgrade the procs to 2x X5365. I had already done the 64b firmware and installed an SSD, Mavs and a upgraded video card. Is it possible to mount more than 4 drives in the MP1,1? What is the largest single drive this update will recognize?

Hi Recently I bought a Mac Pro 2.1, I was thinking of upgrading my GPU to a AMD Radeon R9 280X. According to this post (Part 6.1) https://forums.macrumors.com/threads/gpu-compatibility-list-for-cmp.2174600/?fbclid=IwAR0nX-9bjZ2ydvPBVUIttmrzJ1_3d703TcAWSUycj9xdJ76tcUR0-k7B8_k My current specs...