@longwave, i've got enought power with my 13m + surfboard to ride most of the time. Difference beetween 11 vs 13m² for the low range is around 3-4 knot (on a surfboard).
Personnaly i move from element v3 13m² and buy nitro 4 16-12-10m² for caribbean because Wind is often light
Best match for you could be 9 -11m² element v3 + bigger Nitro (14m²) for light Wind condition or helium 18m² ! With that configuration, you should be able to enjoy surfing condition, and play in real Light Wind when needed !