Which Groupset?

No. Well, to some extent it is when you're in a hill climb competition, but 90% of the weight is rider and of the 2-3% which is groupset, the difference between the top groups and the equally functional third tier ones is only about 10%. So, in the most extreme case, getting the lightest groupset gets you about 0.1% performance gain. You can get more than that from cleaning your chain :-)

Or eating less junk food as I am trying to do...