I need a little help thinking this through...

I want to make my own handles/grips for a pistol and based on the shape of the cut out I am wondering if it would be smarter to use a patern bit off the exact size or use a bushin setup?
I have not used bushings other than for dovetails and need some advice on how to figure out what size I would have to make the tempete bigger or smaller. I would like to use a 1/8 or 1/4 bit for the routing, deepest I will be cutting is 3/8.

(.-.)

I need a little help thinking this through...