Hi
They are pretty close sizewise but the P4 is a little smaller and a lot lighter. It's a touch lower as well.
They're quite different. The MK-IV has much more low end torque but the P4 feels faster through the turns. On the street the P4's mechanical FI takes some heal and toe to keep from stalling and it's sequential gear box, you have to go 3,2,1 to get 1 takes remembering. The MK-IV will pull away from a stop in almost any gear but under 4K the P4 makes little torque.
Best