I would use two packets, and no it's not over pitching. I have used yeast that was less than recommended by my software, which resulted in off flavors, but haven't seen any problem with too much yeast other than drying it out (way more than 2 packets worth). Years ago I read that if there was too much yeast, the beer would ferment out too quickly and you wouldn't get the character of the yeast. But after pitching huge amounts of slurry yeast, I found the beer comes out dryer, but has plenty of the yeast character. If you want a malty beer that isn't too dry, you should use the Yeast Calculator.