The biggest advantage to the narrower q factor in my opinion is that you can more efficiently run the entire cassette range from either front chainring. The narrower stance on your pedals doesn't hurt things either in my opinion.
As for compatibility sram has a pdf which explains how to measure your frame to determine which crank set you need. It can be found here
I was running the 09 Noir's and had lots of clearance on my Titus but couldn't clear the 156's. The only way to really have a good idea though is to measure out the frame based on the SRAM tech doc. Clearance for the crank is mostly dependent upon your drive side chain stay.
the 156 and 166 q cranks both use the same chainline, so the ability to use the whole cassette while in the big ring doesn't change between q-factors. the only reason to run the narrower q-factor is if you like to pedal with your feet closer together.
the q-factor on a truvativ noir crankset is 172mm. 172-156=16, 16/2=8. the arms are the same thickness between noir and xx therefore you must have 8mm of clearance between the inside of your noir crankarms and you chainstays for the 156 q xx cranks to be able to be installed. you'd then want a few more mm clearance to account for small amounts of flex in the crankarms/chainstays during riding otherwise you'll definitely get contact. i'd suggest you want at least 12mm between noir crankarm and chainstay to safely fit the 156 q xx crankset.
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