Yep, viking war + Slayer GP can be an incredibly fast deck. You just have to realize that you go face or lose. If you start trading out, you will almost certainly lose as your opponent starts putting out higher-value creatures for more mana.

Going second can be tough, but you have enough blitzers to help. One card to consider is Viking Longship. Often overlooked is it's ability to give flank to others. Crash it into a frontline and then the rest of your board can go face for the win.