Believe me when I say it's all about the enclosure and a subsonic filter. Bottom line is the box is the factor that will determine, the most, how a sub sounds and how long it will live. Sure, excursion, power handling, sensitivity and of course the amplification and equalization being used all play a part, but the enclosure is the one factor that can allow a great, expensive, bullitproof sub to sound like crap and blow up, and an average one sound great and handle good power for a long time.
As for the Sony's, Xplod subs really work well in properly designed ported enclosures when coupled with a subsonic filter. They handle a fair amount of power, have decent excursion and are put together pretty well (bumped and vented backplates, quailty materials for the spider and voicecoil, etc.). I put P5 subs on par with the entry level JL stuff but for a tad bit cheaper.
Don't go cheap on box building. Get a real enclosure designed by a real installer with good enclosure modeling software. Personally I like the sound of ported enclosures and almost always recommend them. That's where a subsonic filter is so important. If a shop says they don't use a box building software program or they don't know what a subsonic filter is, RUN. Tell him what kind of music you listen to and get a real custom built enclosure for whatever woofer you buy...