It's a bit close, but in my experience, you're better off upgrading materials even if the one you're already using is a masterwork. I'd rather use a normal quality iron sword than a masterwork copper one, for example.
For sharp weapons: silver -> copper -> bronze/iron -> steel -> divine
For blunt weapons, just reverse the above order.
Quality goes like this:
(https://i.imgur.com/SpzsmZi.png)
So you can see that even for blunt weapons, higher quality is still better, though not as useful as on a bladed weapon. And, furthermore, a copper sword will never be as good as an iron sword, even if the iron sword has no modifier, due to the inherent differences in the metal.
However, a masterful copper warhammer might be a better choice than a normal silver warhammer, due to the fact the silver warhammer is only denser than a copper one by about 1.5k density, and if your warhammer skill is low, that 2x to-hit modifier could save your life. If you're a legendary hammerdwarf though, definitely better off with the silver normal quality warhammer.
tl;dr Weapon material matters much more than quality, quality is just a nice bonus when you happen to find it or something to obsess over in fortress mode