Magic Pen Marks are always necessary. MS Quints are great for ganking, chasing, and escaping with Katarina. Scaling health seals are good for about the same as a ruby crystal late game for 216 health at level 18. Flat MR Glyphs help you tank a little more damage early game, which you need to get through to mid game where Katarina shines. Right now I switched scaling health for scaling armor, 27 armor at level 18, which now outperforms flat armor once you're level 6. The point of all these runes is to be faster, gank, chase, escape, close gaps, and stay alive longer. At level 18, if you go warmogs as your last item, with my build here, and when you're elixered up if you get that far into the game, you should have about 3400 HP and close to 700 AP with Katarina. Pretty great.