I own the older model LD41 and have gifted a TK41. I would base your choice on size and weight. If throw, runtimes or brightness are critical for you, the TK41 would have a huge edge but at the expense of more batteries, more spare batteries to carry along, being heavier to hold etc. The TK series also have a more rugged build quality than the LD or PD series but don't get me wrong: the LD lights are built pretty well too.
I am not sure how you intend to use the light and how far you'd expect to shoot a duck down. Do you plan to fix the light on your rifle? I have no experience in that department but I suspect the TK41 would be awfully heavy and not easy to fix on any gun-mounted rail: maybe you want to take a look at TK15 or TK22.
2000 feet is 600 meters and I imagine downed deer in vegetation would be hard to spot even with a TK41 which out of the two is definitely your best bet for that kind of distance!