The truth on low efficiency speakers like B&W?

I've been learning a lot lately, but I'm still questioning the true amp requirements for speakers such as B&W 802s. I've seen mentions of using 45 watt tube amps all the way up to 600 watt mono blocks. Seriously, what is too little and is a 600 watt amp over kill? Can the speakers ever be pushed hard enough to overcome an amp like the Parasound 2250 with 250 watts/ch @ 8ohms and 400 @ 4 ohms? Is heavy bass music require the upper ends of power? Thanks. Owners please chime in with issues you have had with low power amps.