Out to about 500 yards, I can shoot a pretty light rifle Had a Kimber Mountain Ascent with a lightweight scope. Combo was under 7 pounds. Fine to about 500 yards.
Out to about 900, I want a heavier gun. Both of my long range hunting rifles are between 9 and 10 pounds with scope and rings.
Beyond 900, I use a really heavy rifle (15 pounds with scope and suppressor.) Never hunted at 900+, but if I were to do so, I'd want a really heavy gun.
My current long range "mountain" rifle setup comes in around 9.7lbs. Bare naked rifle with mag 7.25lbs, scope 17.5oz, supressor 9.7oz, bipod 13oz. It's pretty easy to build a sub 7lb complete package but not that easy to shoot it. Ultralight anything is almost always a compromise in one aspect or another. Sometimes it's worth the trade off but in many areas ultralight becomes counter productive. After lugging around a competition rig at nearly 17lbs, my 9.7lb rifle feels like a toy.