Everyone needs to remember that Buck lead Bennet by about 3-4 for the last month of the Colorado race. This isn't going to be over until its over. Granted, Gardner seems to have momentum, but I wouldn't make a prediction about this race based on polling unless Gardner leads by about 6 or 7 consistently.
Among legit pollsters - CNN had Buck up 1, and so did PPP, which is within the margin of error (anything goes, including the 2 point win for Bennet), If PPP says Gardner is up 1 in their last poll, it's still an anything goes situation.
But if legitimate pollsters continue to show Gardner up by 4 as it closes to election day (just outside the margin of error), I think he's got it in the bag.