I do like the idea of a used Ti bike, but, buying a frame and retrofit with used parts can be a PITA. My now retired Trek 2.3 started with a replacement new frame from Trek, and, the build out with mix of new & old was pricey. Looking back, I would have sold the frame and bought a new complete bike.
Back to Ti bikes, I looked at Philly Craigslist and was amazed about how many complete Ti bikes were available at prices far less than $2k. Frame should last forever, the original owners took a major hit in depredation with the development of carbon frames. the Ti window as a prime race bike was very short. As they were high end frames, the components generally match the frame quality. I did test ride a used LeMond Ti and gave it some serious thought but it did not have compact cranks I need for climbing. I'd have no qualms about older Dura Ace or Ultegra group set especially if speed to follow TT bike is a prime need. The larger chainring of a traditional crank set is better suited for speed.
There is a special place in my heart for those who ride more of the classic frame like TI or steel. That said, my new ride, a BMC Grand Frodo, recently purchased from
@Ron would do an excellent job to chase a TT or do gravel. Some tire modifications would be required, but, if your aerobic system and legs are good, riding in the low 20's is doable.