You can calculate the speeds, but testing with GPS and a temp gun is how I usually roll. Just so many other variables. My Senton takes off like a plane if I attempt full speed. Running bodyless is a different story.The stock Senton 3s BLX with the standard 20t pinion should top at around 55 mph. @Rich Duperbash is running Granite wheels so that would bump the stock setup to 66 mph. Going with a 3050kv motor and Granite wheels would put it at 63 mph. To get that setup down to 55 mph you would need a 17t (53 mph) or 18t (56 mph) pinion.
For the stock Granite/BRCC, the max speed is around 49 mph. Going 3050kv will lower it to 47 mph. Go with a 16t pinion to gain back the 2 mph.