Look at stack and reach. Stack describes how tall it is, reach describes how long it is, when measuring from the bottom bracket - so with the assumption that your saddle position is adjusted to be the same relative to the BB. There's some good articles on slowtwitch.com explaining the concept.

From your geometry charts:
BMC: stack 574 reach 395
Cdale: stack 580 reach 387

You would describe the Synapse as more relaxed than the BMC.

The Cannondale is 6mm taller and 8mm shorter, if you put the same spacers, stem & bars on it. If you already have a super short upwards-pointing stem and a huge stack of spacers, this frame might help a little, but the two bikes are within a CM of each other in both directions, so unless you are at an adjustment limit on the current bike, it's a lot of $ to pay compared with getting a higher stem and maybe some shorter-reach bars.

In any case, a good professional fit might be the place to start - I would definitely invest in a fit before a frame, or the chances of ending up with a second bike that doesn't fit are non-zero.