I am running FM on a 2009 MBP. I can run about ±15 leagues with decent loading times. I never play a lot of leagues to be honest, so I can't judge about 50 leagues selected. But I can imagine my machine would not like it.
I am running FM 12 on a macbook air and run around 20-30 leagues per save... no problems for me and i have been playing fairly regularly since release.
Same as the other comments, using FM12 on a Macbook air since release, no problems installed via steam - works smoother than any previous version IMO without any problems.
Finally portable FM
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