Obviously Fire I followed by Fire III via firestarter is more dps than hard casting two Fire I. My question though is that since Fire I has a travel time, and I can almost always start casting another Fire I before the previous fire lands, should I be doing that and then using firestarter procs or should I literally be waiting after every Fire I cast to see if firestarter procs and using it appropriately?
Things I have read says it is better to precast your next Fire and pick up your Firestarter proc after that cast. I don't know if that's 100% accurate though.
To save on MP, I'll start casting Fire1 and then move a step to interrupt the Fire1 cast to use the Fire3 if Firestarter hits. The Fire3 goes off instantly and you can immediately go into Fire1 again.
No, the amount of time you waste waiting every single Fire I cast is not worth it. Furthermore, you waste even more dps if you interrupt a half-finished Fire I to cast the proc. Finish your current spell, then use the proc.