I dont know what you mean by "best", but there are many other options available for eg: ams catted dp's and one member here has Noelle Motors dp's, which are modified oem dp's with smaller cats, those would be the best IMO, as they would have OEM fitting and OEM 02 sensors locations!
FYI, x6m SS catted dp's require heat shield cutting + 02 sensors extension cable
So if i were you, i would cancel SS order and contact Noelle
http://www.noellemotors.de/en/home.html" rel="ugc" target="_blank">http://<a href="http://www.noellemot.../home.html</a>
I am sure germans are more efficient than italians
http://f10.m5post.com/forums/showthread.php?t=921223