couple things to consider.
The 7WSM has proven to be a barrel burner while the 300 WSM
has proven just the opposite and goes 2-3x the normal mag barrel life. We have tried them and shoot well but sure go thru barrels compared to the 300.
New barrel will be $500 installed.
Now BC will go from .66 area to .73 or .74
Add cost of dies etc?
Is that jump in BC really worth that much money at twice the rate of a 300 WSM. If so, go for it, if not then I would stay with the 300.
As for the conversion, you have two ways to go.
1. Straight 7 WSM, which is new brass and stock dies.
2. 7/300 WSM which is existing brass and custom dies.
Brass is cheap!