The tire brand and duro has very little to do with it, track size and tightness of turns dictate rear stagger, for that small of track tight turns go with it 1.5 " min to 1.75 " would be good starting point.
In my opinion, stagger is determined mostly by the radius of the turns at your track. I have a spreadsheet that works in Excel, that can easily determine the stagger `for your kart for any track. It's really simple. It's called "nine sheets". It's free along with a bunch of other stuff. Email me.