"The place that you want to get with your playing is to where you are uncomfortable with how far you've gone."
The only way to tell if you are playing a passage too loud is to play the passage too loud. If you are practicing, the only true way to evaluate the sounds you are making is by recording yourself and then listening to the recording.
Whenever students begin studying with me, almost to a person they are uncomfortable at first with how far I ask them to take things like dynamics and accents. You don't know how much dynamic contrast is too much dynamic contrast until you have captured yourself playing with too much contrast via a recording.
When I first joined Boston Brass I regularly found that I was uncomfortable with what I was hearing on my side of the bell, especially concerning the amount of front to the notes and accents. But when I listened back, I found that I was simply matching Rich Kelley on the trumpet or JD Shaw on the horn.
The proof was in the recording and it turned out that my comfort level as it related to what I heard on my side of the bell was not only not relevant but had to be actively ignored in my pursuit of simply "making it sound right."
What in your playing do you need to take too far?