Dungeons and Dragons

My group had 6 for a campaign and it was a bit of a slog, but once we found a good rhythm it ended up being really fun. We set some ground rules, especially for combat, where you had to be prepared and we'd set a time limit for turns. It kept the game rolling and kind of added a sense of urgency, which was an unexpected bonus. Plus, our DM was pretty lenient on things to let the game flow. He said he'd rather let some small things slide for the sake of time.

We also prioritized having a face character for non-combat situations and kind of had a buddy/group system when it came to exploring, looting, etc. That way you're dealing with less instances of decision making that could potentially slow the game down.

As long as players stay engaged while it isn't their turn and are prepared for their own, it should run smooth albeit a little slower. We had a couple players that were not super experienced and sitting down to explain the flow and order of things before hand helped them find their rhythm.

One added bonus of more people is that the excitement level increases in high intensity situations. It's cool when someone rolls a nat20 with 2-3 other players, but it's even more exciting when a table of 6 jumps up from an awesome roll or whatever.

Have fun and good luck!