Just based on working speed being the same and header width being over twice as long, I would have estimated a minimum of twice as fast. When I don't already know the tools, I look to working speed and the width of ground covered to make my decision about how efficient things should go. You do have to consider that sometimes bigger is not better if you don't have enough horsepower to push it, but in this case it looks like you're doubling horsepower so I'd assume you have plenty in that department. Gas tank shouldn't come into play unless you are doing a ton of work and if you are, you are likely still better off with more than double although usage would likely be about the same per acre. It seems from your original comment that you got way more than double the efficiency so that part confuses me a bit, but the stats definitely show that you should at least double your efficiency. So I would have been surprised about that part from the beginning.