Funny in windsurfing how so often a simple "one liner" question
can't really correctly be answered in a simple one liner..
Simple one liner: Yeah it works OK!
Other factors not included in simple one liner..
You will definitely get some moderate performance gain on the Kode103 in marginal conditions by upsizing sail to 7.0 and fin to 33cm. What you want and how you intend to use it (Intended ride style?? freemove vs semi "slalom" ) is also a factor (103 decked out with larger sail/s+fins tends to more freeride and less "wave/move" mode, you get the idea..); Do you really want to set the Kode up for outboard straps /freeride? ... or does the inboard freemove/wave setting (albeit a bit compromised for marginal) actually ring your bells a bit more allround?? (valid options both ways !)
How much and how "worthwhile" the "upsize" gains will also influenced a little by some other variables like rider weight (sail wise you're getting to the upper end of the sweetspot range and the closer you get to the end larger of the sail range, the less "comfortable" (balanced) bigger sails will be are earlier for heavier riders (extra rider weight takes away reserve buoyancy from combo etc) - ie : many bigger riders might consider that 6.5m is about the larger end of the sweetspot, whilst lighter riders may happily go on to 7 or 7.5m (noting too that the gruntier the sail model/tuning vs sail size can also make about 0.5m difference in this discussion as well....ie NCX might "feel" a bit bigger for the given m2)
Fins ; in that combo you will definitely dig out some more bottom end on a 33 than stock 30 (given the bigger fin of same family/power vs size) ratio, however fin "style" as well as rider weight and ride style starts to come back into the discussion as really big /powerful riders smashing chop mercilessly on a powerful vertical 33cm fin in a US box might not be the best recipe for longest life and happiness..
Busy week, I guess you got lucky and scored both the long and short of it!
Cheers ~ Ian