Classical power lamp has a very dynamic sound. Your Marshall (for example) will again sound like a classic British power, with literally "jumpy" as a spring, and the dynamics of fast attack. With all the benefits and features EL34, just a version of the JJ you do not hear the lack of dense low frequencies. Also, lamps are widely used in audio amplifiers, hi-fi and hi-end class for listening to music.
Like all power-lamp during the operation can reach high temperatures and will serve much longer and retain its characteristics, subject to the necessary warm-up, ventilation and absence of vibration amplifier housing.