I think NBME 7 was particularly well-regarded before 11/12/13 were around. Because of that, it has more votes in that poll and a lot of general support around the Internet. Among recent test-takers, my impression is that 11/12 have been considered to be the best predictors.
That said, my scores were about the same on 7 and 11. 11 was a bit higher, but that's probably because I took it a bit later. And my score on 12 was a lot higher, but that's probably because of 1.5 weeks of DIT in between 11 and 12.