Aiming for 200lbs and then deciding if that works seems perfectly reasonable to me. Build makes a huge difference, both bone structure and muscle mass. I know that 166lbs at 6' sounds quite light to me (that's only 16lb more than I weigh as a woman at 5'8"!) but it might be absolutely perfect for some guys depending on build and muscularity. I think you'll have a better idea when you get to 200lbs--at that point you can assess whether you want to weigh less, maintain that weight but lean out, or maybe try to put on more muscle mass.
I think we get an idea in our head of what we "should" weigh--especially common for women, but I think men experience it too although sometimes in different ways (often relating to how muscular they should be). Aiming for a goal along the way and re-evaluating seems healthier than aiming for an idealized number that might not reflect what healthy looks like for you, whether that's higher or lower than the target.
“If I didn't define myself for myself, I would be crunched into other people's fantasies for me and eaten alive.” --Audre Lorde
You know all those pictures of Adam and Eve where they have belly button? Think about it..................... take as long as you need........................
My dad is 6'2" and 175lbs, he's been that same weight since college and he looks pretty skinny. Not buff/strong, and not a string bean either, just a normal healthly looking guy in his 50's. On the other hand I am the same height and body type as you, and at 18 years old, 195lbs, I was sub 10% body fat while working out 20 hours a week and eating like a horse. I looked pretty good and I don't mind tooting my own horn about it. Now I'm at 200lbs and comfortable. I could stand to lose another 10lbs to get the definition really showing, but where I'm at I'm in better shape than 90% of the people I see, and that's good enough for me. I figure if I want to change body comp I'll do it by doing heavier deads & squats, move those lbs from my gut to my ass in a good way.
Depending on your fitness level 200lbs is a good target, but you may want to re-adjust based on how much muscle mass you actually have. Having gone from 230 back to 200, I was suprised how much flab was still there. Good luck and keep it up!