As my understanding (very limited, just putting it out there) goes, this is further complicated by the fact that most jet engines you see (on commercial airlines for example) are turbofans - they have an extra set of blades in front of the main jet engine which pulls cold air in and around and straight out - this part is much more efficient than the main jet at lower speeds, and gives the whole thing a higher efficiency across the speed range. So while the jet itself isn't super efficient when throttled at lower speeds, the fan part makes up for that.
Sorry, bit of a detour off the topic :\ also: [citation needed]
Sorry, bit of a detour off the topic :\ also: [citation needed]