My first real road bike was a CAAD8, to really get the right size you need to know his measured inseam, not his pants inseam. Indeed the CAAD8 is a little more aggressive, based on the CAAD10, so if it's a commuter I'd say go for the Synapse. Try to get better components than Sora if you can afford it. BTW, my 61cm CAAD8 is for sale