hi there would like to know if anyone have tried both units need to know the the IQ btw these two lens here is wad i found to be difference other than its build weight (due to VC) but i also found the marco is 1:4.5 (Non vc vs 1:4.8 (VC) . if u notice theres is more group and elements in the lens(for vc ,is it for having it for better IQ ?) after looking at some small reviews etc some commented the focusing speed improve ?

17-50 vc
Model B005
Focal Length 17-50mm
Maximum Aperture F/2.8
Angle of View (diagonal) 78 45' - 31 11'
Lens Construction 19 elements in 14 groups
Minimum Focus Distance 0.29m (11.4 in)
Max. Magnification Ratio 1 : 4.8
Filter thread 72mm
Length 94.5mm * (3.7 in)
Diameter 79.6mm (3.13 in)
Weight 570g ** (20.15 oz)
Diaphragm Blade Number 7
Minimum Aperture F/32
Standard Accessory Flower-shaped Lens hood
Compatible Mount Canon, Nikon (with built-in AF Motor)

17-50 non vc
Model A16
Lens Construction (Groups/Elements) 13/16
Angle of View 7845'-3111' (APS-C size equivalent)
Type of Zooming Rotation
Diaphragm Blade Number 7 (Circular apertures)
Minimum Aperture F/32
Minimum Focus Distance 10.6in.(0.27m)
Macro Magnification Ratio 1:4.5 (at f=50mm MFD 0.27m)
Filter Diameter 67
Weight 430g (15.2oz)
Diameter x Length 2.9 x 3.2in.
(74.0 x 81.7mm)
Accessory Flower-shaped Lens hood
Mount Canon - Available Built-In Motor Nikon with Built-In Motor - Available
Sony - Available
Pentax - Available