There is a very interesting site in which you'll find all the perf data you'd require at the Eurocontrol BADA (Base of aircraft data ) program.
As a university student you qualify for a free use of this database and it is very thorough on performance.
The graphs for each airplane are given at basically any altitude you' d require (not sure about low level loitering numbers but you should be able to derive your own mode )l.
Look up that site : BADA is here
Note, you have to submit and accept all the conditions, so read the blurb well.
(The data are used for the SESAR European sky project, so the seriousness of the data is guaranteed )