Depends on the aircraft, flaps can make a dramatic difference to the stall speed. Early Cessnas and others designed for stol the flaps can go to 40 even 58 degrees on the Beaver. I have never experienced much stall speed reduction with VG's, couple of knots at best depending on the installation. Some have VG's on the tailplane/fin even on the fuse around the cockpit. VG's do however have an effect on the control feel, they firm up the controls (again depends on installation/kit) at speeds closer to stall.
I've found on many aircraft the original wing performs better without any of the whizzbang additions. VG's, Robertson stol, Sportsman, leading edge cuffs, fences and fancy wingtips, they don't make that much difference, just add weight except to your wallet where they make it considerably lighter 🤣