Advice needed: how to get my interest rates lowered?

I have two loans with NAB: 1. PPOR - >$1m, LVR=60%, interest rate = 6.04% (P&I) 2. Investment - $700k, LVR=80%, interest rate = 6.49% (interest only)

We also have a credit card with them, limit or 15k (as of 2 weeks ago).

Two working parents, combined annual income around 370k. Two kids in childcare.

I call the bank fairly regularly to get my rate lowered but last few times they’ve said they can’t go any further. One person I spoke to even said I’m at the staff rate for these loans. I tell them I’ve got a better offer elsewhere, ask to speak to the retentions team, you name it.

And yet, I see people on here with lower rates, either at the B4 or specifically at NAB.

Is there anything else I should be doing or saying? Or have I squeezed every drop out of this?

Tl;dr - advice sought on how to get a better rate at NAB