Based on your requirements, PEEK filament may serve your purpose. The link presents a glass transition temperature of 293°C, just a bit higher than the 270°C in your post. A melting point of 653° is impressive, but the requirements to print are equally so.

To print with this material appears to require a very specialized printer as well as many cautions presented in the linked page.

Beyond PEEK, I've not seen much that manages the temperatures you require.