What is a safe compression ratio to run with pump gas?

I am currently running 11.5 compression with a stage IV fully ported and milled (68cc) iron head.
The heads have been on the motor for years and are leaking oil down the valve stems and I need to pull the heads and repair them.
The motor pings on pump gas and being that I will pull the heads off I am going to increase the thickness of the head gaskets to lower compression to make it more pump gas friendly.
Here is what I am running now.
R/B block 4.25 stroke 4.35 bore
.613 lift 278 @ .050 cam in at 105 degrees.
Tunnel ram with 2 750 Holley carbs
4500 stall converter with 4.10 gear.
All in a heavy B Body

Is 10.0 compression still pushing it? Or should I aim for la lower number.
Thanks in advance for your help.