The current rating tables are a good starting point, but you do need to take the installation environment into account as well. Most tables are a convenient rule of thumb guide for common types of wire with standard temperature ratings; only the datasheet for your particular wire will be able to tell you exactly what you need to know. The voltage ratings and current ratings are not intrinsically related, but voltage rating will influence the material and thickness of the insulation, which will have some maximum temperature rating. The current flowing through your wire will heat it up, and that heat needs to be released to the environment through the insulation.
In your case, silicone-insulated wire is generally more flexible than PVC-insulated wire and has a wider range of operating temperature, but is more expensive and more difficult to find. You need to look at the whole system to make a well-informed decision. Aside from finding an appropriate wire for the voltage/current, you need to be thinking about:
- Ambient temperature/elevation
- Physical installation: are the wires single, bundled, sleeved, in conduit, etc
- Weather and UV resistance
- Chemical resistance
- Insulation diameter within limits for your connectors
- Flammability/LSZH requirements