You may want to take a closer look at all the stats to see how big of an upgrade the chest is at its cost. I know that the +1 weapon gives something like 2 weapon damage, 5 more vit, 4 str, 4 parry and 3 skill speed. Compared to getting alot more vit (12->33) on the chest and the increases physical/magical armor values (117->158 ), I would argue that the chest is more cost effective.
I got my relic+1 first because I didn't know if I would have threat issues in coil but now looking back I can say that it would not have been a problem and that the chest is the best choice.