what's the diff alpine N872A and AVICs

what's the difference with the costly n872a with a d310 and a pioneer n3 / z1 why does the alpine navi w/o screen or anything else costs as much as an avic-n3? also how does it compare with a z1? I'd just like to know before I buy one and regret getting the other. by the way, how's the speed on these units. when i played with the n2 in a store it seemed slow. what about the clarion NAX970HD i just saw it on a website. it has HDD like the z1

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