@metanoize: If you want a Cannondale SuperSix Evo in a smaller size to handle similarly to your custom frames then the best thing to do is exchange the fork to one with a rake that better suits your desired trail/handling. Perhaps this can serve as a reference (see 'I').
And all SuperSix Evo's are specced with the same fork with a rake of 45mm. I think I understand what the OP is trying to say. If I'm not mistaken Nibali rode a 56cm, so that argument doesn't really hold when specifically addressing the issue of trial and handling.
A 45mm rake fork in a 73º head tube has my preference compared to the more commonly specified 43mm rake, which produces a trail of nearly 59mm. I know the difference since I had bikes with either. Currently, I have an Alpha-Q GS30 with 44mm rake in a Spooky Skeletor with 73º HT angle, which is dead in the middle. It rides exactly how I want it to and is predictable since the bike goes where I point it to without having to "work the bike". If I understand correctly, this is what metanoize tried to illustrate.
Ps. I do feel that the title of the SuperSix Evo being sluggish unnecessarily polarizing, since the bikes handle so differently in different sizes. In fact, a 54cm would be a perfect fit for my 1m83 frame with a required bar drop of about 16cm. Head tubes longer than 140mm make a frame unsuitable for me and are out of the question. I had big problems trying to make my Scott Addict fit correctly until I found a stem of 130x-10º with a low enough stack height, which was all due to the 140mm head tube actually being 1cm higher due to the longer fork stack height.