I had an issue like this for optimizing pgrust. I had an optimization that showed no impact on my test machine (c8g.4xl) and showed a 20% improvement when ran on my mac. It turns out the issue was the instruction cache on the c8g.4xl was being saturated on the test machine but not on my laptop, moving the bottleneck to a different place
If you can consistently reproduce the performance difference, you're already half way there