All true up above however, you forget several important factors. One being Hasselbeck will be playing in a Dome, no weather issues. Another being, Hasselbeck likely to be playing catch-up vs the Rams. All these favor Hasselbeck immensely.
I would take Pennington. The guy does not make a whole lot of mistakes (ints, sacks). Plus I see Hasslebeck getting picked a couple of times and sacked a few times in ST. Louis.