Based on what I want to set up and how I want to go about running my rig, I'm thinking I could start with 8 full Neptune sets or 3 sp35/31. Of course there's a difference in hash rate but the sp35 is newer. Electricity is a nonfactor in my soon to be. (Free utilities, complex probably bundles).

Which should I get? The fireboxes or a lesser hash rate for my investment? ~7-9 TH/s