Last weekend, the 365s from each box (Correa and Pedroia ) had the exact same ratings and skills. The difference for my team was that I had Correa's pennants at 80 and Pedroia's pennants at 40. I played tourneys almost exclusively(maybe 20 prime games and 72 seasonal games). The first 1k games or so, both were d9. The rest of the games, they were both d10(capped Correa once I repulled Pedroia).
As you can see below, there is a difference. I constantly checked throughout the weekend and the difference ranged from .007 to .018, ultimately finishing .01 and always in favor of Correa(the higher pennants). Now, for many, such a difference is marginal and not worth 'chasing,'(i.e fast playing seasonals). For others(like myself), it confirms that I should continue to fast play seasonals. Make of it what you will.
If you're not having fun, you're losing.