I changed the wheels on my Madone for Roval Rapide CLX's at circa 1400g. I intended to swop out the Ultegra for Dura Ace... then decided not to. Why? My 2kg lighter Wilier makes very little difference overall.
Sure, the lighter bike feels better on long, steep climbs and my PR's on those are with that bike...but the Madone is not far away and overall, I think it is quicker as is; I sprint better on it, I TT better on it. It is my preferred bike to race.

I'm currently training for a race next month. I want to drop 2kg...from myself, not the bike where I think it will make next to zero difference to how I do.