I've not built up much of a streak in battle factory but how much of a difference is it usually between the last opponent of a set of 7 and the first opponent in the next set of 7?
On a little side note: a few times by the end of the first streak I've ended up with pokemon such as Metagross and Slowbro, even ubers such as Snorlax and Blissey, albeit with a terrible moveset.