You might want to ask on the kayak forum.
I would think the longer rods would actually bounce more distance than the shorter rods. Of course, the longer rods gets the lures further away from the boat. Myself, I don't like anything longer than about 9 ft in a kayak (but I don't spiderrig from a kayak either).
Handheld gps will work, but some don't read below 0.5 mph. If you are brave enough, I am sure there are cell phone apps that will give gps speed too.