James let me borrow that 203 Donek one morning, that beast rides faster than I ever want to go again in my life! :)
While the length and sidecut are certainly contributing factors, I think what made the Donek such a fast ride for me is that the flex of that board is really stiff; you have to be way on top of it and initiate the turns exactly right to get that board to bend & turn. EC carvemaster James Ong obviously rides it with ease and is able to control the speed, I have a lot of respect for someone who makes riding that monster look easy, in contrast I found it to be demanding and I learned that I'm better suited to a softer-flex more forgiving board.
Compared to James's Donek, my 175 Swoard feels like moving in slow motion, which works out great for me as I like taking it easy. James also let me ride his 186cm, 15M SCR Coiler, my perception is that since it's not a stiff board it can be cranked into similar sized turns, with similar speed, as the 13.3M SCR Swoard, or you can ease into the turn and allow the arcs to widen. I was so stoked with the performance of James's Coiler that I asked Bruce make me a similar one which arrived in April, I'm looking forward to trying it out soon.
Bottom-line, I think for speed control that board-flex is as important a variable as anything else, IMHO only. Rob