I use gamma head tape and I use it from 9 to 3, sometime an inch past the 9/3 positions. I volley a lot and scrape the head even at 9/3 positions.
I think it is about 18-20 inches long and weighs about 4-5 gms. This definitely changes the swingweight for me.
Most guys use a lot less than me.. so it would be ~2 gms for most.. effectively felt at 12 position, which makes a difference.