Compared to NQ, using a piece of HQ gear is like adding one materia to the NQ piece - both make the piece SB 20% faster than a plain NQ piece would.

The reason to use NQ gear though, is simple : you can buy it in Kugane. Take NQ left side gear, stick two Materia in it (as all but the belt has two slots), then make HQ right side gear and stick one materia in the accessories, and you'll SB evenly and 40% faster than the pieces would with NQ and no materia.

Adding in SB buffs may help, but I remember back before HW when using things like +1 or +3 SB on gear really did not add much to the SB'ing at all, and cut down the number of materia you could get per set.