Is it permissible to say the Basmala aloud based on the narrations that affirm it as a verse [of Al-Fatiha], and to say it silently based on the narrations that do not affirm it as a verse of Al-Fatiha, and to continue doing that?

The issue of reciting the Basmala aloud is not linked to whether or not it is a verse from Al-Fatiha. The Hanbali school of thought holds the view of not reciting it aloud at all, even if it were considered a verse. Whether to recite aloud or silently in prayer is a jurisprudential matter that depends on the determinations of jurists and their deductions, not on what reciters adopt. Jurists have differed on this issue: some have recommended reciting it aloud absolutely (like Al-Shafi'i), others have recommended reciting it silently (like the majority), some have held the view of not reciting it at all, and some have taken a middle ground. An ordinary person should follow the jurist he trusts. The audible recitation of the Basmala has no connection to whether it is a verse or not. Emulation should be of the mujtahid imams, not of reciters, unless they are mujtahids in jurisprudential rulings.