I play all 5ers (I have 3) and for me, it's not really about the Low B (I often use the low D, but rarely go below) - it's more about the technique of playing [i]across[/i] the fretboard rather than up & down it. It enables me to figure out a way to play a song & then, if the key needs changed, it's easy to simply move that pattern up or down the fretboard.
String spacing on a 5 or 6 is always going to be narrower than on a 4 - you have to deal with it or go back to 4s. I have a fairly small hand and I don't have fingers like sausages so that helps.
Certainly, more amplification would help you. As you probably know, each octave you drop demands twice the power to maintain the same volume, so the low B needs a fair bit of power and suitable drivers to cope.
G.