Everything Blacksheep Josh says is true.
What I have to say is just additive information.
I always suggest reading the Manufacturer's Tech Manual for the woofers before modifying specifications to suit you.
One thing to note, a woofer may say it has a specific RMS rating, but this rating is usually induced when the woofer is in the smallest sealed enclosure possible. The reason for this is because the minimal air inside of the enclosure limits the Voice Coil movement and allows more power to go through it without pushing it beyond Xmaxx. But, as you increase the enclosure size, the RMS ratings go WAY DOWN... So, keep this in mind.
There a few tricks to this.
Small Sealed = Mid to High SPL / Mid Grade Sound Quality
Large Sealed = Mid to Low SPL / Good Sound Quality
Ported boxes are a whole different beast, as you not only have to consider volume, but tuning frequency. With a Sealed enclosure, the volume of the internals set a Frequency of the enclosure, so that is why the size of the enclosure counts.
For ported you make it work for you. Some of the best SQ guys run ported enclosures, but they are fine tuned (28hz) and have pretty low SPL.
Also, another thing you want to consider is Transient Response. A ported enclosure generally has a slow response time around the tuning frequency, so if you listen to rack or some trance music, then I doubt ported will suit you. But, if you listen to hard hitting rap, than ported may be the way to go.
If you get an idea of what you are considering you want to go for, I can help you come up with some ideas/designs.
Currently, I run one L5 in a 3.5 cu' Ported Enclosure tuned to 35hz. I am only running 400 watts, and get more than what I need out of it.