Soft coral are 10-20x turnover where SPS
is 30x or more.
So, in a 10 gallon tank you'd be looking for 100 gph
on the low end of softies. That would make the 425 way over what you need. This will be helped by pointing it up and towards one of the sides of glass to create a more 'chaotic' flow pattern through the tank.
EDIT: This is all really rough though. Your sand and rock will cause much displacement in the tank, significantly lowering the amount of water in the tank. Either way, powerhead will be fine on flow.