As I have never been anything but overweight at my adult height I chose my goal weight by calculating what weight I would have to be to put me in the healthy BMI category.
I'm fairly confident this would be a good weight as my sister (who is also 5'10") looks really good at 170 (12st) although I do have concerns... how much do boobs account for? Sadly I'm stuck at the shallow end of the dream pool with B cup at my current weight, she however is DD+

life is cruel - if I do get down to that weight I can only assume my boobs will also be smaller!
Because I love the little BMI calculator I use I tried to work out what your BMI should be - I guess from your picture you're in your mid-20's? So here is what I got:
Healthy BMI is 25 to 18.5
At 6ft, 170lbs, BMI = 23 would put you in the high-middle end of healthy BMI
185 would be a BMI of almost 25 (24.8), and 140 would be a BMI of almost 18.5 (18.8)
As I've never been skinny I myself will happily settle for the top range of BMI, I find the thought of me being noticeably 'thin' quite weird
