I'm not to sure any front loaded sub can handle the vast expanse of open space well. That being said, without question the Yorkville LS800P will out perform any other self powered sub offered by JBL, QSC and Mackie. I say that from both my personal experience and from reading numerous threads and reviews on the subject on the net. The general feeling by most sound professionals (that have heard them)is that the LS800P is the undisputed heavy weight champion in its class and price range. A few months ago, in preperation of buying new PA gear, I got to do my own side by side comparisons involving the usual contenders The JBL PRX518S, QSC HPR181I, Mackie SWA1801Z and the Yorkville LS800P. I purchased the Yorkies and haven't looked back. Sometimes i wonder why I bought two as usually one will do the job by itself. If you are only going to be using a sub outside, you might want to seriously consider going with a folded horn type sub. Yorkville makes a powered folded horn sub, I believe it is a UCS1P, same 1500 Watts of power like the LS800P but in a folded horn type cabinet. Out of the other speakers mentioned the QSC 181I was a fairly close second. Yorkvilles are a little harder to find, but well worth the search. I've included a link to the Cobra Sound shootout, you might find it interesting.
http://www.cobrasound.com/shootout06