Best guide is simply expirence. Sonds like yoid i about right. Sometimes the fish wins.

If you want to get technical get a good spring scale and set your drag at about 1/3 of the breaking strength of the line. String your rod, tie the line to hook on the scale then pull back until your drag slips at about 1/3 strength of line. If you are using 15 lb line, set drag so when line is going through the guides to the fish your drag will slip at 5 lbs pull. Once you do that you will surprisd at how hard you can pull to only move the scale to 5 lbs.

One other consideration is the type of line and knots you use. Some knots like the Palomar are nearly 100% breaking strength. Others will not hold up so well. Some lines like Maxima are waaaay under rated. i.e. what they call 15 lb test will break around 20. Others like Ande Tournament actually break at or near the stated pound test. Hope that helps a bit.