I'll be the odd one here
both are excellent, but for my personal tastes, the Swan 6.1s (which are NOT the same drivers as the x.2's...similar but not quite) sounded better with slightly better imaging and depth perception than the Rocket 750s, so I went with them. The Swans are brighter while the Rockets are warmer.....some people prefer them one way and viceversa. But both are excellent.
I Prefered the 6.1's to the 6.2's myself, so go figure. Keep in mind the 5.2s will be significantly Bigger in size! here is a pic of the 6.1 vs 750s, and here is the 6.2s vs 6.1s, so that outta tell you how the 5.2s stack up with the 550;s