Potsy, have you been speaking to my wife? You are right of course a few more kg off my body weight would make a difference, but a little present for my Cannondale is not a bad thing.The rider?
The first thing to upgrade on any modern Cannondale is the stooopid BB30 bottom bracket.
Although that won't affect weight, so for the benefit of keeping OT it's another vote for wheels and tyres.
Don't think it matters at my level either, but a wee present for my bike can give me an illusion of going faster.Definitely the wheels..Replaced mine and my bike looks well smart .Not bothered about them being lighter, don't think it matters that much at my level..