120v is 1600 watts and 240v is 2800 watts for a 75% power increase. It looks like you'll save about 20 minutes just on the strike water heatup, then another 10-12 minutes to ramp to a boil. Not only that, you'll have a lot more options for what kind of boil vigor you want. I haven't been too impressed with 7 gallons boiling on 1600 watts.
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Side note. The biggest component to any electrical contractor job is showing up + labor hours for the work. I would ask for two quotes. One should just be a 240v circuit to support the exact needs of the foundry. 240v @ 15amps (preferably on a GFCI breaker). The other should be a 240v @ 30 amp (4 wire to the box) preferably on a GFCI breaker.
The latter can immediately be used for the foundry, but then you'd have the option of a future upgrade to a system that uses a 5500 watt element without really needing an electrician to get involved. If the added cost is only a couple hundred and you can swing it, I recommend that.