I'm going to suggest you're fine with the dry yeast option. Here's a link to a yeast calculator:
This helps you to figure out pitching rates. If you go to the "Dry yeast" tab, and enter your O.G. of 1.065 and a volume of 5.25 gallons, it suggests 13 grams of yeast. An 11 gram packet is pretty close. Now this assumes your packet is relatively fresh, but dry yeast is pretty hardy.
Now if you used liquid yeast, I'd absolutely go for a starter. Again, you can use that calculator to figure out an appropriate pitching rate. In general, dry yeast goes much further than liquid yeast.