I had a similar experience when I was shopping for a carbon road bike. The owner of the store is around the same height as me so she brought in her bike so I could take it for an extended test ride. Turns out that I needed the smaller size and so they put her wheels on the smaller model and said take it for as long as you like. And I fell in love with the bike but didn't buy the test ride (it was 105) so they ordered the ultegra model for me. Then they set it up perfectly and unlike my previous bike, I have no niggling lower back pain.