Remember that assistance work is there to boost one or more of the big 3. If you're pushing so hard on assistance work that your ME and supplementary work takes a dive, then you're doing too much in one way or another on that assistance.
A lot of it will depend on your genetics, training age, regular age, stress levels, sleep, amount of food eaten, type of food eaten, stretching and mobility, GPP, to a small degree the supps you're taking, and the phase of the moon and stars too I think.
Nobody here can really answer that question here but you and it won't even be the same for you every workout. For the most success out of this, you'll need to learn to auto-regulate your training based on the variables above and really work on your recovery and GPP work.
Remember that you can do your accessories (re/pre-hab and extra volume) at home in case you just don't have time at the gym that day for some reason or you just burnt out faster than usual.
The assistance is mostly just there to prevent imbalances, promote hypertrophy, and conditioning if you crank up the volume and lower the rest periods.