The Steamroller has pretty relaxed geometry. Depending on which IRO we're talking about, it may be more aggressive. A matter of preference and intended useage.
Someone else can chime in about spacing on the Surly, but you can certainly use your DA components. Depending on what wheels you get and what the frame's spaced at, you might end up wanting a new BB for a straighter chainline.
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Originally Posted by monkey
You could be doing blow off a dead hooker with a needle sticking out of your arm and you wouldn't get kicked out of Humboldt.