FM's the State of Play with empasis on Climb performance.

[5./JG27.Farber]

the 250 IAS is for sea level, it drops over altitude.

For example the Bf109T

Alt - 0m's
Speed IAS - 250

Alt - 1000m's
Speed IAS - 243

Alt - 2000m's
Speed IAS - 236

Alt - 3000m's
Speed IAS - 229

Alt - 4000m's
Speed IAS - 222

Alt - 5000m's
Speed IAS - 215

Alt - 6000m's
Speed IAS - 208

Alt - 7000m's
Speed IAS - 200


So merely maintaining 250kmh for a 109 climb test is actually not its best climb. Just a thought.