I like that, 6 spikes deep is good. I also usually go 6-8x2.3m spikes deep if it's a sandy area and depending on the supply size would try for a sub1ohm impedance. Good depth usually gets a good Ra reading especially if you can get below the water table. Did you knock them in the old fashioned way with a sledge hammer or did you use a jack-hammer with an SDSMax rod driving attachment? Last time I used a sledge hammer was a couple of years ago on a remote site with no power, I thought I was having a heart attack after the first 3 rods and ended up getting a generator.