When I used to shoot archery for Bear Archery as a pro I was fortunate enough to see Fred Bear's mounted deer collection. Almost every one of them came from Nebraska. Fred knew where to hunt!
We have huge deer in Wisconsin and the in the last few years (due to the hunters managing their own land) the antlers are catching up to the body size. I think the size also has to do with the winter temperatures and survival. It is common to see field dressed deer weigh well over 200 lbs. here. I've seen some up around 250 lbs. That deer would be over 300 lbs. live weight!
Southern deer (including Texas) are small bodied compared to Wisconsin. It makes those big racks look even bigger.
Right now the biggest bodied whitetails I'm aware of are coming out of Canada (and not just Saskatchewan).