fmic inlet/outlet measures

what is in your opinion the right inlet and outlet measures for a fmic on my zs? thinking that the turbo that i will mount it's a garrett gt 1752 and the exit of the turbo is 54 mm. is it worth to keep the original/dark ice turbo outlet pipe on? or it's better to change it too?

from the last news http://forums.mg-rover.org/showthread.php?t=713329&goto=newpost

via IFTTT