It's all on where you want your handlebar height and reach to be.

steering at 72~73 degrees, , 90 is straight up.

so, a 17 degree drop = a horizontal extension

computer-bike guy made a tool to calculate this : http://yojimg.net/bike/web_tools/stem.php

a Zero angle stem has a rise to it, on the bike .

You putting different handle bars on ? you can tour on it as is, maybe swap to a grip/bar end like ergon
http://www.ergon-bike.com/en/product.html?a=griffe




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