My experience. I upgraded my 2006 Gerolsteiner S Works Tarmac last year to the lastest DA DI2, new Boyd 60's etc.
Very nice bike. After a few months I found a 19' rim brake SW Tarmac frameset I could live with. This was a weight
weenie build and slammed. The first thing I noticed was how comfortable the ride was (140lbs 25's 55lbs). Then
how responsive to pedal input. Want to go faster just grab another gear and it goes. Very dramatic difference. I ended
up with a 10kbuk bike for about 7k with all the components I wanted bars, stem, saddle, wheels and brakes.