Scott, the RS SPL meter and whatever other usual culprits there may be, is nothing more than an incredibly inexpensive broadband device whose greatest utility is in setting up a HT. While people use it in other fashions, it was never designed for many of the tasks that people put it through. Also, it's ever so easy to make a completely innocent adjustment, a nudge if you will, that will skew the results. The use of a VOM, which is even cheaper than the RS meter, allows for very unambiguous readings with no more effort than bending one's fat ass down, mine included, to reach the speaker terminals.
Now, I don't know what any one's particular threshold of sensitivity is. I do know that with test tones, you'd be hard pressed to discriminate a 0.1 dB difference. Very hard pressed. So hard that if Jennifer Biel was to promise you could cop a feel if you could, you'd go home feeling yourself. So, if you can adjust things to that net difference without much effort, why not?
When people don't know the levels are different, they very often offer up very different explanations as to what they're hearing be it a more expansive soundstage, darkness, or whatever the audiophile discriptive word of the day is.
None of this btw means after going through this that you won't hear a difference. But if you do, and it wasn't a sighted comparison, then you really heard something and you can place whatever monetary value on that difference you want.