Definitely try the fin upgrade first, you have nothing to lose going that way (one step at a time) because even if you were to end up going to the 7.0m as well, you would definitely want the extra fin (and benefit from the better trim bottom end) . 103 fin I'm using is Black Project FreeWave 30, it's a very "big" (relatively powerful vs cm size) 30, so I would suggest 32 as biggest (same time noting you will most likely get more than just 2cm difference in performance rather than simply mechanical size). For big/ger riders blasting hard on a standard US box, generally not getting too ambitious with fin size is a wise move for long life and happiness..
On the sails if you're mainly blasting, the NCX has a crisper, racier feel (it's a more powerful cut and full mono, the correct mast sets it pretty deep and powerful although this can be flattened out a bit for a more top end/speed combo by the use of an RDM instead ..). Gator 7.0 is full Xply and has a softer, more forgiving feel about it...it's not exactly "ungrunty" especially if you rig/tune it for light conditions, but the same time I wouldn't rate in "more" grunty than a neatly tuned NCX which also has a great "tunable" range for digging both top and bottom end out of the one sail/size.
You can get away with the 7.0, the board won't sink or fail miserably, it's more that the closer any tune/trim comes to the edge of a sweetspot range, the less the % gains (usually) gained by throwing extra sail or fin into it...Law of diminishing returns working again
Cheers ~ Ian