[ZeonOne]

Here is what I am thinking.

From Rank 6 to Rank 7 will takes about 1.5 to 2 months of time.

In 2 months of time, u can get a weapon's skill from 0 to rank 3. If the weapon is stronger in rank 3 in compare to rank 7 of your current weapon, I say it's worth it.

But, if you have rank 5+ in your current weapon, it is hard to give it up.