WH - does your dog stay in most of the time? Does it have a good (but not excessive)layer of fat in the winter?
I had several shorthairs, and all handled the cold just fine. In fact, they loved cold water! After all, Germany gets a lot colder than here. I think many GSPs have had too much English pointer bred into them "off the books" to increase their ranging and style. The English do not have the thick coat that the GSP does. The GSP should have a short, but very thick coat - especially in the winter. Also, when they are out in the cold, they need a lot more calories, especially if they are hunting hard in the cold! I found that peanut butter or peanut butter with rice crispies in a golf ball-sized serving helped a lot in the field to keep their energy level up and the shivering down.
As far as wirehairs go - they are good dogs and probably more true to the orginal breed than most GSPs, since they are not as popular with the non-hunting crowd.