I finally had a chance to run both the arc starter and welder, and am slightly disappointed. There's two issues:
First, the plastic holding the spark gap pretty much caught on fire. There is a fairly easy fix, move the gap to the exact center, and if necessary, add a fan (would also provide some arc quenching=better performance)
Second, and more importantly, the arc would not sustain full power. Without a capable amp meter, I can only guess the cause. I have a feeling the transformer (I'm running only a single transformer to prevent tripping the house breaker), is saturating. The HV arc would stay on the entire time, but the high current arc would only be sporadic, despite the arc distance. I'm going to run it again tomorrow with the second transformer running off a different branch via an extension cord, and see if I can't get an arc to sustain. But it was definately a welding arc.
Edit:
After some reading, I realized saturating a transformer is impossible by excess secondary current draw (it's dependent on voltage and frequency only
) I guess my next option is the second transformer, maybe in series.