I'm a bigger rider myself, and can relate. With rockered boards, and your size, you'd be fine with 160-163 range. I don't see a need for you to nab a 168, especially to learn on. I've ridden both the Merc and the Infinite recently, and both are solid boards. The Merc may be the more forgiving of those two. I know Ride, and Burton both make some quality stuff as well, but haven't spent any time on the boards listed above from them recently.