For the deck screws I highly reccomend an impact driver. Even the 18V Ryobi impact driver will do this job - it worked well for Ned's screwing needs at his shop construction project. In fact, sometimes I wonder whether my impact driver and ladder remember who their daddy is...
The 4 tool Ryobi kit mentioned earlier
18v Driver, Sawsall, circular saw and jig saw (can't figure why they even mess with that dumb light)
has a drill, not an impact driver - and, as mentioned, you want an impact driver. The drill may not work for some stubborn sections (again, ask Ned, but not when his 21 year old indentured laborer is being supported by said protruding screw "holding" up the planking - "Mark, wait until he is down again before pointing those things out!"
) The light is rather useful for power outages and "can't wait until the weekend" auto repair. And for computer upgrading.
I got into the Ryobi ONE+ line some time ago when I was able to pick up a 10 tool set with 2 batteries and charger for $250 at a sale at Home Depot. This was right after we took Zeus (the tan dog) to have his nails trimmed and I was feeling all dejected from his "being flayed alive" noise and needed to buy a tool to make myself feel better. I went planning to get an impact driver (which was one of the ten tools) and walked out with a whole lot more for just a bit more than the cost of a Makita Impact Driver / Drill set. As always, you need to do your own value calculus when planning a tool purchase. I have no complaints about my Ryobi tools. In fact, the light had dropped down from the attic onto the steps leading to the basement (~a 20' fall) and other than the battery popping out, suffered no ill effects.
I recommend a #2 square drive, but then again, I do not have any experience with those newer star shaped Torx head screws. My experience with Torx head is retricted to bolts on my vehicles and they drive me to loud and vociferous consternation. (Hmmm... they're on my Ford, which is like a Lincoln, and while not a hot rod, they certainly have tried to drive me to intemperate behaviour
)
Assuming that shear srength is related primarily to fastener diameter (I know this is a rather large assumption) what size screw or lag bolt would be needed to equal the sheer strength of a 16d nail? Is there a chart somewhere that gives nail and screw size diameters (grrove-to-groove diameter for screws). For that matter, would getting #8 deck screws with, say a 2" long unthreaded shank provide equivalent shear strength to a 16d nail, since the unthreaded shank is providing the resistance to the shear forces? (This question is independent of the availablity of such screws.)