I want to expand my storage to 16gb primarily for HD gaming (which the Neo V does so well). I have been offered a great deal for a SanDisk 16GB card Class 4 and wanted to clarify if it is enough for HD gaming, classwise.
According to the specifications your phone has 512MB Memory, which is quite close to the lower limit for actual 3D games like N.O.V.A.3. Because the OS must read the game data into the allocated RAM for the game-process (a lot less than 512MB). The game-data is propably bigger than the total allocated RAM space so Android starts to cache the stuff internally (Internal Flash space, not SD Card).
So after loading the game the SD-Card class/speed isn't the most important part. A faster SD-Card will probably just speed up the loading progress but not the gaming experience itself.