Saolboarder has it right..... your weight, and the normal conditions (windspeed, chop height, currents,
etc.) will help us to give you a spot on answer.
That said, a 6.5 m2 would be a good step up from a 5.4 m2 rig.
Not sure you need the multicam Overdrive, but they are good sails and not to hard to rig and
At some point, when your skills develop, unless you are a really heavyweight, you will want larger sails for the GO 151. Probably a 7.5-8.0 m2 and maybe even an 8.5-9.0 m2 to take full advantage of the GO 151's early planing capabilities.
Hope this helps,