I personally have 15’s (sig Zulu 9) and my hunting partner has a viper 15-45 spotting scope. His scope is surprisingly clear (newest model). He spent 99% of his time on his 10’s. My time was almost 50/50 between 8’s and 15’s. This was on a rifle elk hunt in fairly open terrain. Archery elk I only pack the 8’s and a tripod. Mule deer / antelope my buddy used his spotter almost as much as his 10’s. Definitely good to have a mix of different glass for the type of hunt. I would definitely reach out to Leupold on those BX-4s, it’s actually a pretty solid binocular. Something is off if you have a headache from using them.