There are a couple problems with using wheels larger than a wheelbarrows. A larger one will roll over stuff better, true. However, to get the most benefit from the cart, the weight needs to be over the wheel, not behind it where much of load is carried by the user's arms. To get a deer over the large wheel, it's going to have to be considerably higher and that really screws with the balance. A top heavy cart is miserable to use.
