Dave
Silva-Cote is no longer "potential" for UFC 90, it is a done deal.
Diego-Alves is not yet formally confirmed (so far as I know) but everything I've read says it is pretty much going to happen there.
To answer your question - huge. MMA just got sanctioned in Illinois recently and this will be the UFC's first ever event in Chicago. With Silva headlining and two top-7 WW's in the world fighting in a co-main event, it will be a
huge event. It could well break various gate and attendance records; it'll at least test them.
I live in KC, about 8 hours away from Chicago, and will be driving in to see this card. My first-ever live UFC event. I am fired up
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Jackson's Submission Fighting (est. 2000)