I know what you mean. I am not sure what my practical limit is yet, it's still going to take a bunch more testing to get a reliable understanding of it's limits. Measuring something and sticking it out there to range is one thing, being real close with a guess of the actual size could be quite another, and probably disapointing if the range was far enough.
I don't seem to have too much of a problem getting a good measurement in MOA from the R2 reticle, if the target's still, but knowing exactly what size it is definitely can throw you a curve ball.
At a certain range, 30 yards is going to be too much to be off on even larger bodied animals. Add a slight MOA measurement error to that, and one might find an additional 20 yards of error. 50 yards of error would severely limit you in range, even with the flattest shooting cartridges. Depending on ones skill, 50 yards of error might be the best you could do, or it might be 20 yards... There's quite a few variables that could screw a guy up by themself, not to mention the combination of variables that could possibly stack up against you. A really good question. I'd love to hear more about it too. Here in the next year or two, I'll definitely know where my limit with it will be.... wish I knew now tho.