eyeinthesky : I think you will find that most military jets are exempt from the 250kts rule.
The CAA appear to recognise that many of these aircraft do not fly too well as low speeds.
For an L39 Max level flight is 405kts
cruise is 295kts
max possible speed is 910kmph or 491.4kts or Mach 0.8 of course this would involve some height loss. above this speed the airbrakes pop out to slow you down.
To relight the engine with the emergency fuel circuit by windmilling your airspeed needs to be 450kmph or 243kts
The gear can be lowerred below 340kmph or 183kts
You may lower the flaps below 325kmph or 175kts
To raise the flaps you must be exceeding 250kmph or 135kts
On take off the speed during the climb should be 350kmph or 189kts
To do a loop or a half cuban you need an entry speed of 600-700kmph or 324kts to 378kts
To find out more take a look at
military jet partnership or the US site
39th Aggressor Squadron