I would think that you should spend the money on forged pistons and while you have the motor apart you may be wise to increase the end gap on your rings. Anytime you increase combustion temperature it is better to have more endgap. I would not be surprised to see more stock piston suffer the same fate. I have had the same thing happen to a piston in my old 5 litre motor that I was running N2O on, I never heard detonation yet the ring lands were broken just like yours. Remember just because don't hear detonation doesn't mean it isn't happening.
