Two more graphs, real data.
As others have noted here, the 390 manual says 105 lbs of fuel per hour is the minimum for rated power, or 17.5 GPH. 29.92"hg and standard density is assumed in order to achieve rated power, so if it's hot outside, or the aircraft has climbed a bit, fuel flow should be less than 17.5. And Lycoming didn't pick the figure without consideration. It assumes the worst case pro-detonation operating condition, specifically 475F CHT, 245F oil, and 100F inlet air.
The chart below is a mixture sweep to determine detonation onset, again using an IO540K. Chart in the previous post was full throttle. This one can be seen as a condition just a bit into initial climb, as MP drops to 28", with everything really hot departing a quick turn fuel stop in the desert.
As before, 0.50 BSFC is just on the rich side of maximum power. More important (at least to Lycoming's lawyers) is the margin between 0.50 and detonation onset at about 0.44 BSFC. Point is, there is no reason to think you need more fuel to avoid detonation. Lycoming's recommendation of 17.5 GPH already added the margin...and remember, it assumes worst case temperatures. Want absolute max power? It's found a little leaner than 0.50, and given a good cooling system, it's safe to go there. Keep temperatures down, and the detonation line will move to the right, or disappear entirely.