Ummmm ... 
"A second question: the ST60 wind has relative and true wind, but it seems to compute the relative using speed data from the paddle-wheel, rather than the more accurate GPS speed. Which means you don't get relative wind when the paddle-wheel transducer isn't in place. Can you change which source the wind instrument uses for speed input?" Just to be clear. The ST60 measures Relative Wind and Computes True Wind. Relative Wind is the same as what your windex shows. You don't get TRUE wind without the speed input. The True wind that the boat sails in is NOT the same as the True wind that would be calculated from the GPS. GPG SOG and COG can be used to compute True wind relative to the ground. That is not the same as True wind relative to the boat. The boat sails in the True Wind relative to the water. True wind relative to the ground based on GPS input has very limited use. The GPS speed is not more accurate. The GPS can only measure Speed Over Ground not speed through the water. GPS speed and heading information is also suspect at low speeds due to the normal position error. Each 1 second fix has a 10m (33ft) possible error. At 7 knots a sailboat is only moving at about 12 feet per second, less than half the error. GPS speed and heading is a calculated value based on time and distance. The boat has to move more that the error before the data is valid. The Navman wind instrument can be configured to use either transducer speed or GPS speed. I don't know about the ST system for sure. ST Autopilots use transducer speed if available, then GPS speed, and finally a owner preset of average cruise speed if no speed input is available. At lower speeds the AP moves the rudder further for the same course change than at higher speed. Providing GPS speed to the sytem as a back-up is good. Using GPS speed as a primary input can lead to errors.
"A second question: the ST60 wind has relative and true wind, but it seems to compute the relative using speed data from the paddle-wheel, rather than the more accurate GPS speed. Which means you don't get relative wind when the paddle-wheel transducer isn't in place. Can you change which source the wind instrument uses for speed input?" Just to be clear. The ST60 measures Relative Wind and Computes True Wind.
Relative Wind is the same as what your windex shows. You don't get TRUE wind without the speed input. The True wind that the boat sails in is NOT the same as the True wind that would be calculated from the GPS. GPG SOG and COG can be used to compute True wind relative to the ground. That is not the same as True wind relative to the boat. The boat sails in the True Wind relative to the water. True wind relative to the ground based on GPS input has very limited use. The GPS speed is not more accurate. The GPS can only measure Speed Over Ground not speed through the water. GPS speed and heading information is also suspect at low speeds due to the normal position error. Each 1 second fix has a 10m (33ft) possible error. At 7 knots a sailboat is only moving at about 12 feet per second, less than half the error. GPS speed and heading is a calculated value based on time and distance. The boat has to move more that the error before the data is valid. The Navman wind instrument can be configured to use either transducer speed or GPS speed. I don't know about the ST system for sure. ST Autopilots use transducer speed if available, then GPS speed, and finally a owner preset of average cruise speed if no speed input is available. At lower speeds the AP moves the rudder further for the same course change than at higher speed. Providing GPS speed to the sytem as a back-up is good. Using GPS speed as a primary input can lead to errors.