Gem Dilemma

I have accumulated the necessary Telluric Pearls to craft a Legendary Gem.

I have the option to get a BSJ to upgrade my existing BSJ to rank 4. I do also have my eyes on the Starfire Shard to use as a brand new gem replacing Viper's maybe. Have recently been thinking to upgrade my Roiling to Rank 4.

Confused a lot. Any guidance would be helpful.

Thank You