If choosing between two Rapidfires, go for the Koa deck, it's just beautiful. I got one and the top deck still looks to be in somewhat pristine condition (some footwells and pressure dings sure but nowhere near as much nor deep as on my last PU of similar size), whereas the RF bottom does seem softer and less durable than the top deck.
And as iggy said, the Koa was a special edition and therefore it could be in higher demand if you decide to sell it later.
I'm your weight, a lot shorter as evident from my sig and low intermediate. 604 floats me fine, but if there had been a 606 in Koa, I would've probably bought that one. I have Rusty R1 Futures thruster setup and I think they work great.