What should I buy as my step down board?

Hi, I’ve recently been trying to get more into short boards. I ride logs a lot. I’ve been using my friends 6’10 board to start off with. It’s very thick, like 50 liters. I think I’m ready to go smaller, I just don’t know how small. I want something faster and something that I can move around better on a wave. How short should I go? What brand should I look at? What boards should I be looking at?