You should be fine. Illegal volume is defined by the sound ordinances where you live. Usually if other people can hear it fairly loudly then you're probably too loud.
-Nate
As long as you're careful and smart, you should be the fine. W7s really let you know when they are bottoming out...
And another thing, it's not the bass songs that are 'illegal,' it's the volume at which people listen to them, so be smart with that too
-Nate
When the beats are very fast, it's hard for even the best sub to hit every beat very quickly and with a TON of loudness. It also might just be the nature of the bass in the song; it's just not supposed to be as loud as other songs.
-Nate
the W6v2s, not W6s.
if you're on a budget, the O series does nicely if you want to send it ~600 watts.
if you're looking around 300 watts, i suggest the ed K series, IDQ, adire shiva, etc etc.
-nate