I've run six MSR trials now. Unfortunately, only one had more than five teams. I've been having a lot of difficulty recruiting for the MSR trials the past couple of weeks, due to a combination of issues. Mostly due to the Halloween event and competition from the multiple Hamidon raids that are ran nightly on the Excelsior server. In any case, that one league with six teams had no issues zoning in. The only issue was someone thinking the door at the Vanguard compound at Point du Hoc was a trick-or-treat door and zoned out when he or she clicked on it. We'll see how it goes in November.
I did notice issues with inviting people to the league once inside the instance though. Before and during the Pylon phase, no issues. However, it's a crapshoot once the actual raiding of the mothership commences. Sometimes inviting people into the league works, sometimes it doesn't. Regardless, the last zone MSR I've done was back in September, and I don't foresee myself doing one ever again.