If you are wearing a Tec vest, even a bigger pack isn't too bad. I have a bad back and even with an ABS 30 I can make it through the day.
I would agree, I wear a tekvest and a BCA Float 30 all day long with no issues.
The tekvest distributes the weight of the pack across your upper body instead just your back and shoulders.
As far as smaller packs, I also have a Klim Nac pack. Nice nice pack that will carry the essentials and is very comfortable with or without a tekvest.