They are so vastly different that you can't fairly compare them on the same hull. The GPU would be for a smaller hull, lighter built and overall lighter weight. Your Caddy would be the ticket for a larger hull, longer hull, heavier hull.
If you rigged both hulls super light as you would for the GPU then the Caddy wouldnt perform because its weight and power would constantly be deforming the hull and and degrading performance. If both were on the heavier hull built for the Caddy, then the GPU is at a disadvantage and wont perform to its best abilities.
If ya got the bigger heavier hull go with the Car Motor, if ya got a lighter smaller hull, go with the GPU.
In the last analysis, its all up to what YOU want YOUR boat to do.
Scotty :wink: