CAAD vs Allez: Geometry

Jon_1976 Posts: 690
edited February 2013 in Road buying advice
I'm currently riding an Allez but planning to get a CAAD 8 (or maybe 10) instead. I've read the 8 has a more relaxed geometry compare to the 10, How does these geometries compare to the Allez? My current bike is a 54cm and looking at the Cannondale site, a 54cm for either CAAD is the right size. So its the headtube lengths that differ mainly:
Allez - 145mm
CAAD 8 - 155mm
CAAD 10 - 140mm

I use the Allez with the one 5mm spacer above the cone (as opposed to the stock 20mm) and I dont find the geometry aggressive at all. Would the extra 10mm of the CAAD 8 make a noticeable difference? I'm not sure the CAAD10 is within budget so I'm edging towards the 8, provided it isnt too upright. Unfortunately, I'm unable to test ride either as all the local shop are out of stock so it'll be an internet buy.