It's a tool question and what you are willing to buy or afford. If you can go router, I would. At the other end and the old timer way would be cut line close and use a file to clean to your reference line. The really patient chraftsmen can do the one swipe and stand back to analyze. The sheet metal department at my old airline would have rough cut and then trimmed to line with a die grinder and sanding or scotch brite wheel.