The Sigma lenses are lighter. Even some of the Nikon ones are as well. If you can find a good used price, the difference between an f1.8 and an f1.4 can be bigger than you'd expect, in terms of working in low natural light and also regarding lens sharpness.
Eugenio Upright, 60th P-Bass, Select J-Bass, Geddy Lee J-Bass, Yamaha BBP35, Viking Bari
Select Strat, Select Tele, Am Pro JM, LP 57 Gold Top, RS520T, T486-RB, ES295, PM2, EXL1
WX5, XK1c, Voyager