Even at 3/4 fuel it substantially lags the 66 for in cabin payload when float equipped, at only around 776lbs allowed. And now you are well under 300nm range as well. Not to mention OGE performance of 7600ft vs. 10000 for the 66.
That seems like a rather draconian trade off. Just out of curiosity, if you don't mind sharing, what are your payload and range requirements?