Based on your criteria, I find it hard not to recommend the drivers I'm using.
http://aespeakers.com/shop/catalog/product_info.php?products_id=68
They are incredibly articulate, and Ive experienced a pair of these running in a very decent setup. They are incredibly clean, match your spl criteria no problem, and I havent heard anything as clean (although my experience obviously cant include everything). They will come well within budget and the only area they might push your limits its size, but not by much. They work well in a 75-125 litre enclosure with QTC ranging from .707 to .6 respectively, although you may wish to employ a filter for the larger box sizes to help protect the bottom end excursion. As a side note, there were no apparent issues with the ones I heard in 125 litre enclosures so me personally, I wouldn't be overly concerned and especially at the levels you wish to run at.
http://aespeakers.com/shop/catalog/product_info.php?products_id=68
They are incredibly articulate, and Ive experienced a pair of these running in a very decent setup. They are incredibly clean, match your spl criteria no problem, and I havent heard anything as clean (although my experience obviously cant include everything). They will come well within budget and the only area they might push your limits its size, but not by much. They work well in a 75-125 litre enclosure with QTC ranging from .707 to .6 respectively, although you may wish to employ a filter for the larger box sizes to help protect the bottom end excursion. As a side note, there were no apparent issues with the ones I heard in 125 litre enclosures so me personally, I wouldn't be overly concerned and especially at the levels you wish to run at.