The circumference of your 2.75 tire probably has more affect on performance than the weight of it - it will bog down your acceleration but you would have better top speed when you get there, eventually. Consider a smaller front sprocket to compensate, it's way cheaper and easier to deal with than swapping out Gazelles.
I use a cheapie 41 chain to dial in what's best then switch to 420 chain for the long run, because 41 chains stretch a lot and will wear the sprockets pretty quickly. Stick with a good quality 420 chain, any weight savings will be minimal at best for performance.
BTW, my Free Spirit is currently running 16T front and stock 45T rear sprockets with NOS Semprit 2.5 rear tire on an otherwise completely stock setup (with over 12,000 miles - cases never split, never touched the clutch) and the bike does pretty well with urban traffic.