Here is the noise spectrum graphs of the two models operating at identical MIC input gains, and comparison of LINE input noise using low noise external preamp for same MIC gain.
Comparing the noise performances of these different models over frequency is possible with eyeing the dB scale numbers at the right to the graph lines showing the recorded deck noise levels.
How audible, or interfering to the audio signal purity a deck's internal noise is going to be depends on the frequency, the character of the noise (like is it continuous Gaussian type or more audible digital impulse with harmonics) and the dB level (loudness-amplitude) of the noise.
It does seem, at least from see the graphs, the D50 has the quieter analog inputs.