You may be able to start with a bow under < 4 lbs, but you won't be able to finish with a bow under that weight.

You would be talking about a difference of maybe 1 - 1.5 lbs across the board for compounds, but once you add quiver, sight, rest, stabilizer, and any other trinkets you will be up around 6-8 lbs.

Bout the only way you can get a smooth light bow is go traditional - barring that go with a bow that fits you and that you feel most comfortable shooting - the weight will not play as big a factor as feel!