It supports about the same size groups however bigger groups are better than smaller groups. Every single monster in Hackmaster (5th) is super deadly as both sides roll attack and defense and damage dice penetrate. Also taking large hits can cause you (or the monsters) to go into shock and be out of combat for large lengths of time.
Its easier on the DM's side because the DM doesn't manage everyone's initiative. They manage what the monsters are doing and they manage the second that the combat is on. If you act on second 12, you had better announce our action when the DM says "Second 12".
Combat is extremely fun because of the amount of actions that you can take, attack defensivly/aggressively, jab, jump back... and the critical charts have you roll a d10,000. Critical also scale with the amount of damage you do and with the amount that you hit by.
As for 4th edition, its amazing as well. Super spoofy. With a table for EVERYTHING. I think there is a set of tables you can use to generate an entire random dungeon. But that combat is super close to 2nd edition.