E. Zegna for Saks. Different than E. Zegna with no Sak label?
A pic of the label would lead to a definitive answer but if you are talking about a Saks labeled suit with a separate label for Ermenegildo Zegna fabric ("tessuto"), then there is a difference. If you are talking about a suit labeled Ermenegildo Zegna for Saks, then there is no difference between that and a Zegna suit (not taking into consideration the different quality levels/country of manufacture of Zegna).
Ha sorry I was not clear. It is a mainline zegna in every way as far as i can tell (construction and fabric) with a Saks Fifth Avenue label in additon to the normal Zegna label stitched on the inside, purchased a regular Saks store. I was just curious is the "Made For Saks" is of any significance with respect to the quality of the garmet.
No. "Made for Saks" is just a way for Saks to get its name in the garment. I have a solid navy Canali suit that says "Canali for Mitchells of Westport" (http://mitchellstores.com/) on the inside of the coat and the suit is a Canali in every possible way - it just also says Mitchells. I think you can be confident that the suit is a standard Zegna make.