slow games and the people that make it happen. Options

[Maelstrome]

one of my friends runs sr4. he stopped running because his group takes forever to do anything. they argue about who should do what and whos idea is best. they have no team cohesion. it got to the point where a run that should have only taken 3-4 hours went unfinished after 7-8 hours of play and had to be picked up later for another 4-5 hours.
the gm had planned 12 mission it took them 6 sessions to do 2 of them. those sessions where over the course of one month. the gm was fed up with it and quit. i suggested to the gm that he take a prewritten adventure and run it for his normal group and then run it for me and my friend to see which group did it faster. when the group started my friend and i were in that group but we quit due to "conflicting interests". the gm declined the idea. later the friend had the idea that we play the part of recurring antagonists or rivals to his current team in an attempt to straighten them out.we are making our new characters and will probably play later this week or next week.

anyway, what would you do if your players were like this? how would you handle another team playing recurring baddies in your game?