Pulling wire rope so it's tight?
Put the crimps sleeves in place with the screw eyes apart the distance of the poles minus 1 inch (1/2" for each side) and fasten it all together. Set one eyebolt into the post all the way in except the 1/2". Important, count the full turns it took top get the eyebolt in that far. With the other eyebolt in place on the cable, twist the eyebolt counterclockwise the amount of turns it took to get the other eyebolt in, then add a few more turns if possible. This will insure the cable has the best chance to be tight when you are done. (This is what the 1/2" extra on each end and the extra reverse turns are about) It may take a bit of effort or extra help to control the reversed cable, but start it in the pre-drilled hole and turn the screw in. That should get you tight, at least as much as 2 wood posts will allow.

I did this with concrete threaded inserts on both sides of a concrete wall and 1/8" stainless steel cable between them, and they got bowstring tight. I installed about 14 of them in a room for hanging things from.