The CAAD bikes are race bikes and the Synapse is the sit up and beg sportive frame. The CAAD10 is a stiffer version of the CAAD8, so straight seat stays instead of hour glass shaped, and a stiffer frame overall, though the CAAD8 is still considered amongst the best alloy framed you can get
Yeh, you’re right, I thought the CAAD 8 had the Synapse geometry, but I think it’s the same as the 10 apart from the longer head tube.
But who decides that these frames are the “best alloy frames available”? I’ve seen it repeated on here many times, I just thought they hada good rep cos they were stiff and cheap so were popular for crit races.
It seems most of the big manufacturers have a top end alloy frame in their lines now – specialized/giant/canyon/trek etc.