I'd sub out the prisms for something as hearty as your scorpions. Maybe wraithlords and warwalkers with mixed weapons. Wraithlords last alot longer than tanks do, and you definitely want support that can be in the fray, which prisms cannot. I'd say, take a pair of warwalkers with bright lance/starcannon and a wraithlord with whatever you think you are lacking, instead of the two prisms. Remember, your infantry needs support it can count on, and two(or one if you focus) prism shots might not be what the solution is.
You could probably pack all starcannons on the walkers and a brightlance on the wraithlord. People might scream cheese, but thats all your distance AND power shooting. That would definitely lighten heavily armored squads(or light) and the brightlance for the passing tank.
Of course, you could just take a Revenant, but that's a different story..