Why only 1000 watts... I'd shoot for 1500 - 2000 watts.
For sound quality, sealed will help you. Also, going with subs specifically designed for sealed enclosures will help too. Almani S7 might be something to look at on a budget.
I used to work for JL... I don't know if this is still one of their design goals, but they used to design their subs for a higher than average -3db down point, around 60HZ, to squeeze as much SPL out of them without any noticeable drop in sound quality... maybe look for woofers which fit that profile... you would have to start loading woofer specs into a box program to find them.