canklecat

I wouldn't worry about maintaining factory spec unless it was a collectible groupset. I'd rather set up the bike to suit me than to match OEM specs.

As I mentioned about my '93 Trek 5900 OCLV, it's a mish-mash of top shelf components from various manufacturers: some Dura Ace, some Dia Compe, and titanium bits from Chris King, White Industries, American Classic and Ibis. Trek could easily have specced the entire frame with all Dura Ace, but instead they went for the lightest available components regardless of maker or cost. In retrospect an all-Dura Ace bike might have been considered more collectible. But in terms of making a high end road bike for serious mountain stages, they took the smart choice by going for the lightest bits and bobs available.

It's the sort of thing you'd see nowadays only on bikes custom built for short, steep hill climbs, like the British hill climbing competitions in autumn, Everesting, chasing KOMs (actual mountains, not KOMs on flat terrain, downhills and that 100 yard segment between city stoplights), etc.