I don't trust human estimation for something that needs to be as precise as simfile BPMs, unless you use a tedious trial-and-error approach. (And even if you do use trial and error to fine tune it, it's best to start reasonably accurate). For best accuracy I would say to either drop the file into MixMeister or open it in something like CoolEdit or GoldWave and carefully highlight X beats in the waveform and use that to work out the BPM (although there's still an element of estimation in that, so I generally prefer to just use MixMeister unless the answer it gives me makes no sense)
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