The latest flight prediction for GAGA-1 based on an 0900 UTC launch has it flying for 3h04m and reaching an altitude of 35km (114,000'). The precise altitude will depend on how much He is put into the balloon on the day.
The predicted landing site is in a field east of St. Neots. Of course, that is subject to change based on the maximum altitude, the performance of the parachute, the wind speed, etc.
Technical information about the launch is in my previous post. All amateur listeners are welcome!