Ray,
check the cost between screws (especially GRK) and spikes -- not even close.
You can get the material predrilled for the tying spikes. I don't have a source for the material or any practical experience, as I've so far gotten out of it everytime I've looked at a job like this.
I've heard nightmare stories from guys I've worked with about warped and twisted 3x decking, so make sure you are getting good stuff.
I would rather supply and lay 2 layers of 2x decking -- is that an option?
