In reality you can exceed the max rating by some with no harm (say 800ml or so). Most of the concern of overloading has to do with the structural integrity of the lift and motor unit housing, which on the CPE2 system are fairly delicate.
That said - i would never run more then 1L over time, as that is sure to shorten motor and PC board life.
If you want to stay with the 2500 system reels you have:
You can use a smaller 2500 system tank, such as the multitank 5 (2550) and run up to 5 rolls of 35 or 6 120, and use 640ml, which is close enough to the stated max rating of the machine. Or the Multitank 6 (2560) for up to 6X35 or 8X120, with 850ml.
Then you will also have the 2521 for smaller runs if you want.
Swapping to the 1500 system will save you chemistry, and will always be under the stated max capacity for the same quantities as the multitank 5. You can make a larger combo (1510+1530+1530) for up to 7X35 or 10X120 but then you will be using 800ml, still better then the 2500 system, and not so much more the max capacity.