Nokia Belle FP1 has some added improvements which include Dolby Surround Sound, Improved web browser and new maps. The Nokia Belle FP1 update will also make it's way to the Nokia 603, Nokia 700 and the Nokia 701 making it an exclusive to the 1GHz powered handsets.
These three handsets will also receive a tweak to their processors which will be clocked at 1.3GHz from their current 1GHz speed. The Nokia Belle FP1 update which would like not have any visual changes is mainly aimed at improving the user experience on the Nokia 808 PureView and the other 1GHz lineup of devices.
Nokia confirmed that older devices including the Nokia N8 and the Nokia E7 flagships wont benefit from the Nokia Belle FP1 update. It is questionable if they will see any further OS updates from Nokia given their hardware limitations.
source - Nokia Conversations