by Peter W. Tue Jan 09, 2018 2:55 pm
The very short answer is: It depends.
Resistors have two functions - one obvious, one not-so-much:
Function 1: Act as a current limiter, voltage-divider, or voltage dropper under specific conditions, depending on 'where' in the circuit. This is mostly a function of resistance, with current rating being chosen for the minimum 'safe' amount and tolerance dependent on the specific need.
Function 2: Act as a fuse. In which case, the tolerance and current rating will be chosen with equal care.
The bean-counters will not tolerate expenditures beyond what is absolutely necessary (dependent on several parameters not discussed here). $0.00001 does not seem like much, until multiplied many thousands of times across many thousands of parts.
So, in direct answer to your question, you will need to determine:
a) The consequences if the resistor opens.
b) The consequences if the resistor *does not* open.
Writing for myself, I tend to use, exclusively, 5% resistors-or-better, and I tend to take the time to further match across channels. But as to wattage, I am far more careful. To use a solid-state example, too high a wattage on some resistors in the venerable Dynaco ST120, and a spike will destroy the driver and output transistors. SOMETIMES, however, the resistor will fail first. However, in most tube applications, higher wattage *is* better. On the FM3, one resistor as-supplied is 2-watts, and runs at about 1.9999-> watts. Going to 5 watts is a very good thing.
Ignore the bean-counters. Look at what the resistor is doing, and size accordingly.