"We" got into a huge mess about this some time ago. A 1/8 hole is NOT going to affect coolant flow to any measurable degree. What it WILL do is GUARANTEE that air will burp out the top of the stat. Years ago, I nearly "het up" my 440 when I installed the Sig cam. Fortunately, I thought about checking the heater, even though it was about 80* in San Diego, and NO HEAT. I quickly shut it down, removed a heater hose, and proceeded to put in some more coolant.

Getting all the air out does two things
1. It prevents having to watch the radiator neck for when the level drops which means preventing scalding burns in bad burping cases. That's good enough for me. I've seen it happen and heard about it hurting others.
2. It fills the engine completly, meaning the engine isn't subjected to hot spots, overheating and then a rush of cold coolant, meaning more shock.
You can slowly fill it andd let it sit overnight, recheck and refill in the morning and it should be fine. I'd rather be sure I'm not going to get burned and risk engine damage, plus, I'm usually ready to fire the engine after filling...