Went 3 full league seasons, so 114 (38*3) games unbeaten with Southampton in FM12.
Lost in the CL and cups obviously, but unbeaten in league.
My team was just full of insane regens by then and there was literally no other team challenging me - United and City were both way down the table, with my main rival being Newport County :L But even then it was way too easy.
I find FM13 harder to go on massive streaks as I always seem to get one inconsistent result like a 1-0 loss to West Brom at home or something when I've won my last 15 games.. Highest on FM13 is probably around 20..