I would be quite surprised to find that there isn't a CF bike out there that would match or exceed your beloved Boreas. I've ridden enough CF bikes to know that there are vastly different ride characteristics. While BluesDawg points our frame geometry as a major factor in handling, there are other equally important variables. With any modern frame material it is possible to build stiffness, horizontal and vertical compliance, and other characteristics into a frame depending on how much of the material is used in different places and different ways. So, I doubt that it's just a material difference between the two bikes. One other very common adjustment that can cause wildly differing handling experiences is the headset. I know from several first hand experiences that over tightening the headset can change a bikes handling characteristics from stable and predictable, to erratic and very unpredictable. So, I would respectfully submit that a more accurate statement might be that you prefer the Boreas over the Giant TCR. (Please note that I have no vested interest in any frame material given I have bikes of steel, CF, and alum. and love them all.)