Why do 2 different online active filter calculators give way different GBW requirements for the same frequency range?
Without knowing details about your filters (topology, gain, approximation), the &quot;required&quot; GBW depends primarily on the required accuracy of the filter function. Of course, an &quot;ideal&quot; opamp would be best - however, it does not exist.
Therefore, we require an opamp &quot;as good as possible&quot; under technical,  economic and application-specific considerations. In this context, it makes no sense to ask for an accuracy that is better that the unavoidable tolerances of the passive parts (R,C), which may be different for the variuos applications. More than that, some filter topologies are more sensitive to GBW limitations (multi-feedback) and some other are less sensitive (Sallen-Key, GIC-structures).
Therefore, it is common practice to consider a certain &quot;safety factor&quot; as far as the recommended (or required) GBW is concerned. And it is no surprise that each filter design software will contain its own &quot;safety factor&quot;.
Comment: Instead of a cascade of 4 second-order stages, a direct realization might be better - starting from a fully designed passive RLC bandpass of eighth order.
There are different strategies to convert such a passive filter into an active realization.