I am thinking of using this to re-sling...
I am thinking of using this to re-sling older Chouinard hexes bored to accept 8MM/9MM cord. Is this stuff stiff like Titan or the old 5MM Spectra? Would it be better to just use 8MM static with a 12KN MBS?
This would be fine. The 4800lb breaking strength is 21kN, which is more than enough. The 8mm stuff wouldn't slide as much in the holes though, which could be a bonus.
It's important to note that the breaking strength for static weight is 4800lbs but this does not directly translate to a dynamic force. Since this uses non stretching material for its core a fall would only have to generate 7.2kN to break this stuff.
It's super safe as an anchor or for other static purposes when used with a dynamic rope but should not be used as a rope or personal anchor point.
As for this exact question, this SHOULD be okay but you have to be very careful when modifying gear like this. Creating burns in the hex could easily shred the cord.