This is just my personal opinion, so take it with a grain of salt. If you are asking about which sub you should buy wanting to push 4k+ to it daily, then you are just asking for trouble. Start off with something smaller, get a nice amp that pushes around 2k RMS. Pick up a pair of Fi Q's, AA Havocs, DC Level 4s, etc. Do plenty of research on them, build them a proper box, set your gains properly, etc.
I think you will be plenty happy with any of the above, and if it turns out to be not enough for your liking. You'll have some experience on doing it properly and you can upgrade later.