If your goal is 800yards, you will be doing it from prone, so an extra couple of pounds is not a big deal, and will actually make it easier to be more accurate with a heavier more stable platform.
If you go with a 10# rifle all up(with scope) the recoil will be better, shooting accurately to 800yards will be easier, and that is not that difficult to carry a 10# rifle. A 10# rifle can also easily be shot freehand for close range work.
My recomendation is to go alittle heavier than 7#. I don't think you would enjoy shooting the lighter rifle in a 338.
If you go with a 10# rifle all up(with scope) the recoil will be better, shooting accurately to 800yards will be easier, and that is not that difficult to carry a 10# rifle. A 10# rifle can also easily be shot freehand for close range work.
My recomendation is to go alittle heavier than 7#. I don't think you would enjoy shooting the lighter rifle in a 338.