IQ of Panasonic 14-45 f3.5-5.6 vs. Panasonic 12-35 f2.8

I'm not thrilled to spend the money for the 12-35mm, but I can tell you the constant 2.8 is a total clincher for me.  It'll be more useful for my shooting. So I'm going to  save up and do it right (for me)  the first time., and bide my time with the kit lens.