Thanks for the correction, hopefully my statement that I'm hardly a hobbyist makes it clear I'm not super sure :)

I guess I don't understand enough about how this variable sitting in memory might affect hit/miss/alignment especially if it's not used in the program as it's running.

Would it be that some variable that is used is pushed off of a page in memory or something by the unused variable, so access it is slower? I guess that makes sense.