I second the suggestion to use timber screws rather than spikes. It IS a huge time saver, not to mention that they, by design, will not work back out of the timber like a spike eventually will. Yes, they cost a little more than a spike, but you more than make up for it in time.
For a spike you need to pre-drill, or the spike will tend to "wander" out of the front or back of the timber as you drive it. You don't need to do that for the screws.
Use a 1/2" drill to drive the screws, you may have good luck soaping the threads before driving them. I doubt a normal 3/8" drill would handle 8" screws. Some cheaper 1/2" drills may not.
I don't know what you mean by "rough" cut. I don't think I've ever seen a rough cut 6x6. The only thing that comes close is a RR tie, and like I've said, you don't want to use those.
Here's a picture of a 6x6 wall that I did with a few buddies while in school. This is the finished wall. I'll post some more pics of how it went together. It's five courses tall (above grade), with a base course of two 4x6's side by side. I don't remember why we did that for sure, but we did.

It has a deadman in it, though it's not visible from the front. I'll post a pic of how that went in as well.
Dan