John's probably done it or could give some good advice on the combo. He catches both each seasonally down in FL and has probably experimented them together in his tanks.
I would think an 8" knife would eat a 2" pickerel. If it can fit in the knife's mouth it will get eaten. I would not recommend this. The pickerel will also have trouble getting food with a large aggressive tank mate like that. I would put him in a separate tank.
