You can order a brochure from the official WRX Subaru site. I understand from someone that just receive his, that the brochure has plenty of pictures of both the wagon and sedan, as well as specs.
Here are the reported dimensions from the brochure:
sedan headroom is 38.6 (front) / 36.7 (rear); wagon headroom is 39.7 (front) / 37.3 (rear); sedan leg room is 42.9 (front) / 33.0 (rear); wagon leg room is 42.9 (front) / 33.7 (rear); sedan shoulder room is 52.7 (front) / 52.9 (rear); and wagon shoulder room is the same. http://www.imprezawrx.com