thickness

Just wondering what the max thickness board anyone runs on a regular basis is? Was running some 400gsm board the other day without any trouble but was wondering if any problems occur if you go any thicker?

Hi. Thanks for your help. Would anyone know the approximate thickness of both the cover and the inner pages of National Geographic magazine? And how would you describe the quality? Glossy? One more. Do you think this thickness might look silly for 20-25 pages, or would it be OK...