Before I got my 4520, I ran through all the directions I could go if my B21 or JD318 garden tractor died. The only option for replacing the 318 would be the X748. Wanted diesel and 4WD (for the rare but challenging snow removal). So what was up in the air was the 4 wheel steering or not. The turning radius difference between the 748 and 749 was 25" vs 21".
There was a "how close can you mow" spec of 28" radius vs. 6" radius. I've seen a lot of trees with nicked bottoms from the deck hitting it. Around here, a nicked bottom means bugs in a few years, and the tree has a high probability of falling down in 10 years. Now you can have the same damage from a weed wacker too. So the 4WS vs. normal is a how good are you at being careful and what do you do with the areas around the trunk of the tree. You can survive an error or two with a weed wacker, not so with the deck. My choices are also influenced by landscaping that has very few trees to mow around, and my being content with a little boarder of grass around them. Classic lawn-yard-field trade offs. You have to contend with both your aesthetics and those of your customers.
The 7-iron vs normal deck choices are both straight forward and agonizing- how much to do have to cut and how often. The constraint of no 7-iron with AWS compounds the agony.
Steve, based on your picture I can understand why the 4WS is enticing. With the right operator (that would be you), you don't have to go back and do anything where your trees are. No mulch, no weed wack, just trees in grass and mow it, once around each tree and your done. If your customers want closer than that, they can pay for a hand held grass clipper to get the last 1".
If all your areas you mow are this clean and have these sorts of obstacles, I'd just get the 62" deck and save time. If you manage to wear out that deck to the point of you'd have to buy a new one, you'd have to buy another deck but you would have saved a lot of time over the years. Time is a precious thing, and it tends to win out when I'm wrestling with trade offs.
Pete