Ten people will probably give you ten different opinions, but consider that the darkness will vary to some extent in the production process. If this is going to press, the pressman can turn the ink levels up or down and it will darken or lighten, and it would probably look different at different line screens on different paper. And if it's going to be digitally printed, it might look different from one device to another. That said, back in the 90s I used to screen solid images into the background using screen tints at 15%, so if you think 5% is too dark, I think the term "too dark" might be a bit subjective to get more than a general opinion. You may want to consult your printer.