Main differences between the ZT HD and the Pro Turn, or next higher level mower?

I have decided on Gravely but am having a hard time deciding between the HD and the Pro Turn, which I think is the next higher level mower. What are the main differences?



I only have 1 1/2 acres to mow, but it is far from a highly manicured lawn and I want to make sure I buy something that will last for MANY years!