Nitros question

I've used nitros before in my 340 with flat top's. I retarded the timing 5 degrees per hundred horse shot and it did fine. Now, I have replaced the flat tops with 12.5 to 1 TRW's and I'm running 110 octain fuel. I was wondering if any one could tell me how much to retard the timing now per 100 shot...I'm sure it will be different now that I have more compression??

Thanks, Bubba