The flats experiment was definitely a success. I used Fender 9050L flatwounds. I really like the tones I was getting with my Special and the active EQ helps getting a well balanced tone for many kind of music. You can easily go from beefy to snappy.
Despite that, I've found that my StingRay was somehow lacking a little bit of his zingy/aggressive character with flats, it felt like a dog in chain. I ended up putting some Boomers on it and it came back to life.
Like I said, if you like flats I strongly suggest to try a set on your Ray, because with the help of the EQ and its natural bright tone you can make them work very well in terms of versatility. Compared to a passive P (which I prefer for THAT tone), the difference is huge imho.
I just see my Ray as a cannon, and he must shoot hard. I usually choose that bass when I want an aggressive tone, I have other basses for mellow meety stuff.