I think slow play is relative to what's going on for the day. I've played rounds that felt like 6 hours that were 4.5, and i've played 4.5 hour rounds that felt like 3. Anytime you're losing 2 holes though is inexcusable, that's when frustration builds and your game tends to go to shit because your focus is elsewhere. Common courtesy goes a long way, I was playing behind a single a few months back and he was playing multiple balls (badly), he noticed that me and my partner were catching him yet did nothing to let us through. Continued to play his two or three balls so I hit up when he was pretty much out of range. He cracked the shits, got all in my face and I just told him in no uncertain terms that if you're playing multiple balls then it's just straight rude to not let others play through.