Mike,
We typically ride 65-70 at 22 mph. As I'm sure many people have told you, the speed helps, but is by far not the most important factor in jumping the wake. It's mostly in the technique, if you can keep the line tension using a progressive edge, then stand tall at the wake, the W2W will come easily at most normal (18-24)wakeboard speeds.
When it comes down to it, I feel like I need the boat to go faster to help me, especially on TS jumps. Just because I know the 'theory' doesn't mean it comes easily behind the boat
My advice, get an instructional DVD, or better yet, find some riders who are better than you to help you progress this summer. Best of luck