well, if your working with minimal space, weigh your options! can you get away with .875 cu.ft per sub? or would the 10" be optional for the space given? Also have you thought about the Depth situation yet? the W7 is a DEEP sub!! Alot deeper then I expected when I first seen them!

 

Why are you limited to such a small space? Is it a weight issue, small vehicle, need to keep cargo area?
What vehicle are you putting it into?

 

it's going into a 1998 subaru 2.5rs
and ya i'd like to keep some cargo area in the trunk

 

the recomended box sizes will fit nicely between the wheel wells both the 2 8" and the 10" but i'm going to go with the 10" so i'll let you all know how it ends up sounding.

 

Well if it's output and space you're worried about a single 13w6v2 ported will only need a slightly larger enclosure than the 10w7. It will also have better SQ IMO.
You could also keep the enclosure less deep by using a shallow driver like the new 13TW5 due in April which looks promising as it's said to have the SQ comparible to the w6 with great ouput abilities for a shallow driver.

Just a couple more options for you.

For the two setups you've listed though I would pick the 10 ported over the two 8's also.

 

the reason that i was picking between the 10" or 2 8" is because i can get them really cheap from a frineds the 13w6 will set me back more then all 3 subs put together