I recommend getting CM4 and downloading enhancement pack number 5.
Finally theve got there with this 5th patch, ok still a few bugs but its got that gripping addictive feeling that all the other CM's had.
Currently with BHA in the 1st (still) in my 3rd season.
How many leagues are you running?
Are the background leagues set to Full Detail?
What size Database are you using, Small/Medium/Large?
Once these are tweaked the game runs perfectly well.
Currently I have 3 leagues with background ones without Full Detail and a medium database and it runs just as fast as any other CM I've played....and I've played them all!
Plus you get the quality 2D match engine which rocks when Chippy scores a 40yd screamer like he did for me last night