When you say top speed, are you speaking of Speed Step (#125) on a 990 Legacy Remote or more speed to crash and destroy your engine?
Speed Step 125 is a reasonable limit for running my large Vision Line Big Boy engines. These are not race cars. If my Big Boy #4014 crashes, I keep another #4014 sealed in the box under the train table with my 4004, 4012, 4017 and 4018.
Sincerely, John Rowlen