I did the same thing you are talking about doing to one of my ponds a few years ago. My pond was just about the same size as yours. The contractor cut the dam, pumped out the rest of the standing water. The silt will obviously retain lots of water.

The contractor was able to get a low enough slope into the pond that he was able to drive the tractor to the muck grab a bucket load and back out. I was also lucky from a cost perspective because I was able to use the muck to fill in some low areas on my property.

The whole operation took him about two weeks including some reshaping of the banks. One word of advice, make sure your contractor has up to date insurance.

The specifics of your situation might dictate one approach over the other. I was able to have the work done during our dry times. If we had gotten any rain it would have slowed things down considerably.

Good Luck

JW