PERSONALLY I wouldn't go more than 6 inch rods. Just easier to handle in that length. And Tom has a point. Get some magnesium rods as well and get a GOOD Hardened steel striker. I like the firesteel Super scraper and the Palm scraper looks like it might be something nice.

DT made me some Ferro rods with deer antler tips for handles and they are really nice. He also included small aluminum water tight containers for the PCB containers. Works really well and you don't have to worry about them breaking open on you.