Long tubes should help power just about everywhere in the rev range - however, they should be noticeably stronger than shorties in bottom end torque. MM&FF just did a test comparing several shorties and long tubes and the 1 5/8" primary long tubes made almost 40 ft-lb. more torque at 3000 rpm than the shorties. That difference became less and less as the revs rose in their dyno test.
Installation is always a bit different on each car - long tubes are a challenge to install. You just have to decide if you want them or not. Many times motor mounts have to be disconnected and the engine jacked up, or the steering shaft removed and run between primary tubes - depends on the brand of header. Also, if your mounts are old, and the engine has sagged - sits lower in the bay, you may have some clearance issues. It's a good time to refresh the mounts - engine and tranny.
Volume is more a function of the rest of the exhaust system (cats, h/x pipe, muffler type, etc.), but most folks report that the annoying resonance around 2000 rpm is significantly reduced if not eliminated with long tubes. Do some research on the location of the O2 sensors. Installing long tubes usually results in having to move the O2 sensors further back in the exhaust stream, and that often causes some drivability issues for people.