I have adjusted the 727-200's aircraft config.   The thrust scalar to be specific.  I was not really looking for more speed as much as a little better ceiling.   At my FSpassenger wts, I was falling out of the sky at 26,000 ft.  I bumped the thrust scalar from 1  to 1.1 and it does make a good bit of difference.

I should say I adhere to the EPR numbers on this chart
http://www.boeing-727.com/Data/engine/engdata.html  which can certainly make it a challenge.  

If you look at the aircraft config is says a static thrust of  15500 lbs which would make it the  -15  version of the engine.

I did read some former Piedmont Airline pilots speaking about altitude and speed.   very early on they might cruise their brand new -100's as fast as M.8  but that was soon toned down to M.74-.78  once gas prices became a factor. The 727 was certainly not a high altitude aircraft, they said 31-33,000 was pretty common for operational flights. 

As delta dog said, at heavy wts it is a fuel guzzling brute
I think it takes a lot of attention to flight profiles as well as patience to fly it efficiently   To me efficiency is the key to getting the most out of it.  Enough fuel to make the trip with a planned reserve and no more

Anyway, I get around 28-30 thousand ft comfortable cruise altitude and around M.74-75  using the chart EPR and the small change.
Thats close enough for me.  If I did change anything else it probably would not be thrust, I have come to enjoy those long takeoff rolls!