Probably a major consideration is component condition and your ability. The Specialized should have 10 speed Dura Ace 7900. If the components are in great shape and the gearing works for you, (you don’t need to go compact and wide range), it would be a foolish choice to choose a defunct niche brand over the Tarmac.
Even moreso if the Klein has 10 more years of wear. Those old shifters aren’t going to improve over time and you’ll never find replacement hoods for those 9 speed Shimano shifters. I can’t imagine anyone picking a fat tube aluminum bike so every 6 months someone can say, “Wow, a vintage Klein.”
John