I am assuming the same between the Nexus and, say, a Note 4.
I had not really held a Note 4 until today..... It's pretty much the Note 3.. I didn't feel the Note 3 was too big except for my buddy who had his Otterbox Defender case on it (But he is a mechanic so just par for the course he plays) It's still going to be hard to say until you physically have the Nexus 6 in your hand.... The 2013 and 2014 Moto X both feel amazingly small.... The 2013 felt tiny compared to my Nexus 5 and even the new 2014 version actually felt smaller.... The Note feels bigger....
with pretty much the same design language as the Moto X I am going to just guess it's going to feel a little smaller than it is....