Hopefully the original poster is thoroughly confused by now. Now read this:
http://www.codeonemagazine.com/archi...tch/index.html
Now consider that all these limits (low alt, high alt, different configurations or "we just didn't test it") apply to one aircraft.
By the way, as for ram effects: the problem is that sooner or later the temperatures in the engine reach a point where it (in practice) blows up or wears out. Above a certain speed (usually supersonic on a fighter engine) the engine actually has to throttle back to stay within compressor exit temp limits.