As mentioned above...sizing by seat tube does not apply to modern frame design. Some brands don't even list seat tube measurements.
The best way to determine size, is by the stack and reach numbers. These will tell you how the bike will fit, then you can look to the other measurements (heat/seat tube angle, BB drop, rake/trail, wheelbase, etc.) to determine how the bike will feel on the road.
I do think it's save to say that the M/L you are looking at simply will not work for you. So the next step is to figure out if a TCR in a L will work, or if you need to look into other brands, or stick with the Defy that you currently have....we should start with the question, why are you looking to replace it?