Do you have a spotmeter or incident meter? Both these types of metering can ensure you get enough shadow detail. Shots like your nightscapes would be a challenge in black and white because the shadows can be truly empty while highlights coming from neon signs can hit the other extreme.

With a spotmeter, you would choose the "important" shadow. Then (using Zone System terminology) place it on Zone II, III or IV depending on philosophy. When you meter carefully you can use the full speed, again depending on philosophy.

When I say I shoot ISO 400 film at 250, I am spotting the shadows and placing them on Zone II. Someone who spotmeters shadows and places them on Zone III could rate the same film at 400 and end up exposing using the same f/stop and shutter speed combination as me.