What is the purpose of the 8" horizontal spike? Only 2" is going into the next plank, not much holding power there. The double spline is doing the alignment, so that is not it. I would see a GRK doing a much better job. 4" nails going through 3" material also does not offer much holding power, 1"??
When using screws to pull something into place I often wind the screw through the board so it sticks out the far side, this is at about a 45 degree angle, with the plank held slightly off the rafter or surface it is going to be held to, this protruding part of the screw will enter into the approximate area and suck the plank home, bending it to where it need to be. It works most of the time. Something that does not work as well with a spike or nail.
One aspect of the Timberloc screws Brad mentions which I don't like it the washer under the hex head is not very big and can sink too far into the wood making contact with the driver socket a bugger to deal with at times. GRKs have a larger washered head and the T-30 bit fits into a hole and this is never an issue. You would be wanting to use the 1/4" or 5/16" lag screws from GRK.
