I have found that the SQ is very similar between the two (Eclipse may have a little edge, but you'll definitely pay for it) but Eclipse subs are much louder What model of eclipse are you looking at?
The Perfect and the 8700 series are much closer in both performance and price, although the Perfect is still cheaper. If you have the money, definately get the 8800 series.
yeah those 8800 series would blow the perfect's out of the water. i love the way those subs sound, normally i don't like metal coned subwoofer's but to me those eclipse's are awesome in every aspect except for kindness to your wallet