Here are the numbers you need to compare - forget head tube and ETT, those are confounded by head/seat angles and BB height.

BMC
Reach 39.5
Stack 57.4

c'dale
Reach 38.6
stack 58.2

so the BMC is both 1.1 cm longer and 0.8 cm lower.

You didn't answer my question about the canondale setup. If the canondale was set up tall (lots of spacers), you are going to need super-lots-of-spacers to get that position. Luckily, raising the stem does make it a little shorter in the total reach to the bars. So, it might work, but if the c'dale was already topped out on the spacer stack, it might just be too many spacers for it to work. Or maybe you are flexible enough to adjust to a lower position than how you were originally fit. Sounds like you were not really fit anyway, though, you just tried it out.

So if it was me, I would probably get a real fit first, and then decide. Or you could get the BMC and then return it if it doesn't fit, which would be kinda lame for CC, but they do offer that return policy, so that's their problem.

what road bike do you have now, and are you happy with how it fits? Normal amounts of spacers & stem, normal saddle position? That would be another data point.