Shaving off 170 gram swapping seat and 50gram off the seat post ain't gonna do much. Experiment by trying to see if there is any difference riding with a full bottle of water or 1/2 empty.

I strongly believe you gain better efficiency from losing lbs through excercise from your body than off your bike. When you lose those lbs, you make you lungs process oxygen better, your heart strengthen and is more efficient. If you drop 10lbs off your bike, you only loss 10lbs of weight but does little to your body. If you drop 10lbs from your body, you gain better cadio stanima.

I used to be very overweight. I was well over 200 lbs, I cannot ride anywhere even if my bike was 18lbs. I would be short of breathe by the second block. When I lost over 50 lbs, I can ride my commuter bike fully loaded at 45+ lbs with ease.

Lose the weight off yourself first, afterwards any weight shed off the bike make a bigger difference.