God hates a coward, now back to your OP.
You are just going through the white/yellowish cambium layer under the bark. The Beetle larvae actually girdles trees and kills then. You don't have to go deep at all. Too deep with some species can cause snaping in the wind as the SAP wood is the strongest part (not the hardest) A tree can survive by a little thread still in tact of the Cambium layer.
Just saying. I don't have an opinion of how you go about it. I don't have oak experience. Generally with softwoods standing trees like Pine Beetle attacks are dry at the butt in 6 months and the top take longer but Birch, Cottonwood, Aspen are opposite. and defoliate and decompose from the top and take way longer.
I have seen dead white oaks stand for 7-8 years. Start shedding limbs then sapwood decomposes, roots rot and they finally fall over. Have 2 logs right now that died 12 yrs ago and I guarantee they will cut your saw rpm's after the first 2 inches of cut and they laid on the ground for 4 yrs after falling