Here are some ramblings from me on the OP's question.
The first thing I think when I read the first post is this. Put aside the NOS question and look at your statement. You are building a motor that should make 500hp, your rods are rated to 550hp and you want someone to tell you that it will be ok to shoot 50-100 more on it? Plus you didn't even say what specific rods they are.
Hypereutectic pistons really don't like detonation. The guys told you that and you didn't like the answer. Those pistons are pretty good in their intended environment. The problem is that if your tune is off some or you get a little oil passed your rings you have traveled outside of the envelope of safe operating parameters for hypereutectic pistons.
500hp with a small dome and 5140 rods is a good decent running small block. If you want to make 600hp build the motor to do that. Don't try and do it with a 500 max hp build and be disappointed.
This is just my humble opinion so take it for what it cost.
Curtis