I run quite a lot for my spec machine and the game flies tbh, I mean I dont play in 3D or 2D as it bores me, but I can churn out a season in 6-8 hours id say and thats running:
Top Leagues in:
England, Spain, Italy, Germany, France, Belguim, Holland, Scotland, Greece, Turkey & Portugal
Then whatever league im in, I run all their divisions - so in England I have it all the way to the BSN/BSS.
Finally my database is custom with the following; Large default, All Players from Top Division clubs Europe (this means that the leagues im not running will at least have their players to compete in Europe) and All Players from Top Division clubs South America (to find the gems).
IIRC my current save has 85,000 players to start with but I read somewhere that within 5-10 years that number is shaved significantly by around 20-30% due to the regen process.