To clarify what I said:
If the AEQ piece with Vision/Big Hit is for Head, and your standard Head piece is +4 Speed, go with the SV piece, if your standard Head Piece is currently +4 vision, take the Vision/Big Hit piece.
The logic is that SV shouldn't be difficult to find again, and you can likely get it with an attribute or useful %. +2 vision is already a great addition to the Big Hit which you may not find again.
Even though SV is a better SA you will ideally have a AEQ pieces and you can shop for SV + something later on. If however the Vision/Big Hit AEQ piece would replace a standard Speed piece, take the SV.
all imo. Hope that helps.