I don't know if it's 100% realistic since I have never flown a 727 in the real life. But from what I've read and understood, the 727 had a lethargic (don't know a better word   ) climb rate at higher altitudes. It took them quite some time to get up to their assigned crz level. And I would not look at the KIAS when you're up that high, look instead at the mach number . It doesn't make it better when the 727 lacks autothrottles and an altitude selector on the AP  

Yesterday I was flying a european medium haul with the PMDG 737NG (which is said to have one of  the most accurate airfiles for FS) and at FL370 my KIAS was around 250 (Mach .79) with a crosswind component of 66kts. My groundspeed was however 459kts. Keeping in mind that the 737NG is much newer and has better performance than the 727, I'd say your 727 performs well according to the real thing.

According to Boeing a 727-200 cruises at 30,000 to 40,000 feet at 570 to 650 mph (not sure what that would be in KIA or GS at 30,000 or 40,000 - it's probably easier to take it up and look at the readout on the GPS than to try to figure it out).

The panel I'm using is a custom modification that has autothrottle and altitude selection so that's not a problem. I like the panel because it has 3 sets of engine gauges and I have a generic fuel gauge so I can use it with the longer range, higher performance MD-11.

I'm glad to see there is no flaw in the model.  I just have a 1960's aircraft that performs realistically.

Jim,

I also fly the Mike Stone B727 with the Charles Fox revisions for an aircraft gross weight of 185K. Fox revised both the aircraft.cfg and .air files.

I have done some climb testing of this bird, because when I file IFR I want to be sure about actually getting to the requested altitude. My criteria is to climb and accelerate to 300 KIAS while gradually reducing VS in order to maintain the correct airspeed. When the aircraft can no longer maintain the correct airspeed at a VS of 500 fpm, that is my measure of ceiling altitude. In the case of the B727, if airspeed reaches Mach 0.78 then constant Mach becomes the speed control.

My test for a takeoff weight of 185K will get the bird to 30,000 ft at 500 ft/min when airspeed begins to drop off. With only half of the fuel (takeoff weight of 152K), the B727 gets to 38,700 ft. At this higher altitude, airspeed control has switched to Mach 0.78 and Mach number is beginning to drop off.

This is my way of measuring cruise ceiling. We all do it a little differently. That's why I offered all the grimy details. Hope this is useful to you.

Cheers,
JerryH