jl audio 12w6's, how big is too big?

I have never noticed any bottoming out in this enclosure as of yet. but hey thats why I asked if there were any cons.

To add B.J. Fisher of http://www.fishercustoms.com/ was going to build me a 4cf box for these two thats why I opted to build the 4.6 so when I droped in the third sub it would be about 1.5 per sub

So if i were to buid a smaller box do you think I have / should go down to a 2.5 cf box or could I get away with say a 3-3.5cf  and be safe.

12w6excursion.jpg

WinISD Pro shows me, for two subs, 2.5 net cu ft and maxing at 500 watts.  The blue line shows 3 subs in 4.6 cu ft net and maxing at 600 watts. 

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