Yes its that much more. However if you cant fit the proper custom ported box, you'll want to downsize. Box is everything. a pair of 8s in a proper box can destroy a 15 in a shit box or sealed box.
This is far to vague to answer.... 4 planet audio 12" subs vs. One atomic apxx 12" the atomic wins all day.
Need to know vehicle box size electrical amps being used. Box rise is a factor that could definitely drastically change the outcome of each setup as well as frequency of burp or if music is used instead.... tuning is key for all and the answer to this question can be argued way to much from many perspectives