It depends on how deeply you like to hurt yourself.
In a crit, unless you get dropped or you are strong enough to be on/off the front of the pack; the rest of the racers sort of determine the speed. Hang on at all costs. This can hurt.
In CX, you set your own pace... kinda. If you want to hurt real bad, that pace is super high. If you are a wussy, pace is lower as is effort.
Some of my "hardest" races have been 90 minute P123 crits. Much longer than a cross race and I get way deeper into my pain cave as the pride of not getting dropped gets a lot out of me.