Can't answer specifically about Saks suits/jackets. However, I have been impressed by the quality of Saks label shirts and sweaters -- I've got a few of each and they seem to be very good quality -- both the stitching/buttons and the fabrics. I'd expect the suits to be at the same level -- comparable to Hickey-Freeman I would guess.
The Saks private label tailored clothes are not at the quality level of Hickey Freeman. As far as I have seen, they have no handwork, whereas I believe HF does have hand-set collars, sleeve-heads, and a basted chest piece.
Saks had their own factory for Many years. Fashions for men by Dominc Verti(Verdi). It was on west 15th street in NYC. They made a beautiful suit. RTW and MTM. The factory has been gone for many years. I don't know who does the private label. Gittman used to do the private label shirts. Don't know if they still do.