MrMalty says to use 1.1, so instead of using part of a 2nd packet, I'd just use the whole thing. From everything I've read overpitching is better than under, so I try to err on the side of overpitching to minimize off flavors and ensure I have plenty of healthy yeast to do the job. I also can't be sure exactly how viable my yeast is, so that has to be taken into consideration. If MrMalty said to use exactly 1 packet, then I'd say it was close enough and just use one. Ideally I would pitch exactly the right amount.
MrMalty's calculator assumes that you are rehydrating the yeast. If you don't rehydrate and just sprinkle your yeast on top of the wort, you can lose up to 60% viability. That's why you'd go from 1.1 rehydrated packs to 2 packs sprinkled. Yeast isn't that expensive considering the time you spend brewing this beer, and you want to make sure you have enough to to the job right.
**I should add the disclaimer that I am not a yeast scientist or anything, just a regular homebrewer. I'm just relaying the knowledge I have aquired from the things I've read over the years. The rehydrate vs sprinkle as well as the overpitching vs underpitching debates have been going on for a long while, and there are plenty of differing opinions. I just tend to go with the opinions based on science rather than the "It worked/works for me" ones.