New Firmware version has appeared on NaviFirm for Lumia 800C and now for the first time for Lumia 800. It seems to be the chinese variant of the Tango/WP7.5 refresh firmware for Lumia 800 and a new variant for certain product codes of Lumia 800C. The version number is 1750.805.8773.12140. If you remember earlier firmware version number for Lumia 710 and 800C is 1750.800.8773.12120. Since this is the first time Tango firmware has appeared for Lumia 800, it seems software update for Lumia 710, 800 and 800c might be coming very soon now.
Keeping fingers crossed !!