Well, I've been SIC though not in the Gulf, and not until I had almost 1,000 pic., but I'll throw in my .02.
You've pretty much already laid out the pros/cons of the situation... The biggest disadvantage of leaving instructing before reaching 1,000 hrs. is you lack the minimum's to get most entry level turbine PIC positions.
I have no idea how long it takes to get promoted to PIC within the gulf structure but I'm sure this will happen eventually and if your goal is to fly ifr/twins, then this may be a good route. Even if you hope to flight lights/singles eventually, this may work, we'll have to wait for GOM folks to give their input.
A guy I know is leaving instruction for the summer to fly SIC on a fire contract, and intends to return to instruction after the season to build up his PIC. That's an option with a seasonal job, but probably not as good an option for you if your goal is to fly in the gulf.
I would say that either route would be valuable, but one consideration is that there are many pilots already working in the GOM who want to transfer over to become SIC just to build IFR/twin time, but the companies are keeping them flying little ships and filling co-pilot seats with low time guys like you... Since this is the case, if your goal is to get into IFR/twins, this might be your best chance to get in. Having more hours seems to make it harder to land these twin jobs because you're too valuable as PIC in lights.
Again, I don't work down there so I could be way off base...Good luck either way...