You're right, an 8 would be overkill, but you get my point. My thought was going the dozer route, not so much going for an 8. I was trying to be sarcastic and realistic at the same time, didn't quite work in my favor. You're right, an 8 could hog the thing out in not much time at all and grade the spoils out in a day's time, 2 days worth of rental/playtime for someone who has to run through the learning curve.
Legitimately, a D4 with a good operator could bail that pond and grade out the spoils in less than 2 days. The advantage of using a dozer vs. truck and mini is that you don't have a whole wad of unsightly dump piles to knock down later if you plan on leaving the spoils onsite. You can hog the pond and contour the spoils while you're at it with a dozer.
Go hard, go fast, or go home