Is fire longsword worth upgrading to +6? (SOTFS)

Any weapon you like is worth upgrading to +6. You can get infinite large titanite shards really easily in SOTFS. Going to +7 and higher should take some more thought.

The fire longsword is a great weapon and more than capable of finishing the game. You might want to consider switching it to lightning later on, because lightning has less issue than fire with enemy resistances. A good build for the fire longsword would be one that focuses entirely on Vigor/Endurance/Vitality/Adaptability because it only ever gets pitiful scaling from str/dex/int/fth, though it has more than enough base damage to make up for the lack of scaling. Basically consider it the same as a lightning/fire upgraded sword from DS1.

/r/DarkSouls2 Thread