When you say residential, do you mean it's for homeowner use?
Anyway, for less than $7000, I'd recommend you getting a low hour, one to two year old commercial machine. The brands which are popular in your area would be your best bet since there's obviously dealer support already established.
If you spend $7000 on a new mower, you'll have to downgrade in specs. For 7 acres, it wouldn't be worth it. 60" deck minimum and at least 25hp would be my starting points.