I've tried both the K-fins and the WCT (Futures version of the K) and always seem to blow them out of the wave a bit, losing too much drive. At 6'4" and 200lbs, I need the bigger fins to get hold drive without scrubbing speed on hard turns. I'd always used something similar to the large Merrick template in my boards until I took the plunge with the H3s. The H3 template is a big departure from your standard "rakey" Merrick. Given your weight, you may want to look at the MEDIUM H3s. The Large version may have a bit too much grab and might not feel as snappy as you like. Also, I love the H3s, but ride a variety of fins that are all fun on the right board. I still ride the Large Merrick fin when I ride my 6'6" Ft. Knox in GOOD/BIG waves. I have a Surf RX board called the "Flat Day" that works great with a set of Large GMB-5s, and I have a nice FCD board that was feeling a average until I stuck in some Pancho Sullivan Futures and now I love the thing... So, to simplify the matter... the common thread here is that these are all Large fins which equate to my size and style of surfing.
I probably wouldn't recommend the H3s to a beginner, but as an advanced rider you'd probably really dig the medium version in "normal" surf and the Large when it gets over 6ft. I ride my DD with H3s all the time on Pea Island and have enjoyed every session.