Levels are only part of the story. DVD and Bluray let you use right up to zero if you are game. However, how loud do you want it to play compared to say a feature film or TV doco? A feature will have dialog peaking around -30 to -20dfs and broadcast has dialog typically peaking around -10dbfs
Loudness of course, is more than just levels. Is this a mixed tracks with dynamics processing (compressor limiters)? There is also the issue of setting dialog norm values if you are using Dolby ac3.
So what is the content and market place for the bluray. It may not matter what your levels are up to a point depending on that.