I've been brewing with a 55,000 BTU torch burner for five years and haven't felt the need to go to a larger one. I'm replacing that burner with a 60,000 ring burner to give me better control. The burner on my mash tun is only 10,000 BTU. If you are planning on sticking with 5 gallon batches, I don't see any reason to go over 100,000 BTU.
Remember one unassailable statistic, as explained by the late, great George Carlin: "Just think of how stupid the average person is, and then realize half of them are even stupider!"
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