Where do these signals come from / go to?
Diff. pairs have both differential-mode and common-mode impedances.
Ideally, both should be matched to load and maybe source. If these
signals interface directly with a cable, I'd be concerned about that.
Also, what is the common-mode impedance of your termination network?
If these diff. pairs go from IC to IC (which tend to look electrically
like single-ended sources and loads), and each line is terminated,
then maybe you'd want to stick with coplanar edge coupled pairs with
not much coupling.
Regards,
Andy