You are talking sunset when everything gets that nice color right? If that is it, I would use the 400, and try to get my subject to stay as still as possible. Kodak VC for me at least makes well lit Reds and Blues really stand out, if you want balance that blue water, red sky, subject thing use the 400 and maybe a bounced flash or better yet a reflector on your subject if you are afraid of blur. 160 will get you a dark background with just so colors, and a blurred subject unless you use lighting, then the background will really fall out.
Unless you are looking for really deep DOF you will probably be happy with both 160 or 400 for DOF, I know that sounds stupid, but I shoot 120 in a Pentax 6X7 and at sunset the aperture numbers for 400 and 160 are closer to each other than at noon for me. If I want deep DOF at sunset a tripod is involved and no one can be in the shot without flash.