One reason I use a 7-weight in fresh water is dredging deep ponds or deep holes in moving water. The Orvis Depth Charge 250 grain line has a 6-inch per second sink rate and works fine for those uses.
The Orvis Depth Charge Line in on Sale right now for $69.00 - normally $98.00 if you're in the market.
https://www.orvis.com/p/hydros-hd-depth-charge/19bmRangeley Region Sport Shop can order it for you and have it drop shipped to you.
That would give you a chance to talk to Brett or Sue
https://rangeleyflyshop.com/