While I love the POSKY planes in general they do have some issues when it comes to real lifelike performance.
The A330, 340 and older 747 versions where the most notable ones.
Also their 767 is a bit off , certainly when it comes to take-off performance.
Usually this is a direct result of a below standard Air.ed file.
The aircraft.cfg file are rather good only the contact points are a bit odd which may lead to taxiing problems and trim setting issues.
If you adjust the weight settings for load and fuel it usually messes up the Centre of gravity (well outside specs), this is the result of their policy to put the reference point at the nose of the aircraft and not near its static cog point.
A way to work around this is to put only 1 loading point in the aircraft.cfg setting on which you put all the load-wheight, also the fuel position (tank-position) points should be near this reference point , as a result you'll see that even at MTOW the aircraft will stay within its COG-limits meaning that you won't run into trim problems.
Back to the Air.ed file, here are some more issues.
The most notable are the settings for drag for the fuselage, air-brakes and flaps which are either way too high (certainly air-brake and flaps) or a tad too low (fuselage).
Also a very annoying problem are the settings for power behaviour, basically some models have a wrongly calibrated power output (A330 most notably) which means that at eg 85% power the readings on your instruments will say 85% but actually the real output is nowhere near that.
Personally I no longer fly the 767 (excellent model but at 140GB game I have to make choices on what I want to use) but use the A332 and 333 extensively married with Airbus pro panels from PSS
After extensive modification on all previously talked about points (and some more) they fly wonderfully as far as I can tell.
Fuel consumption is very near , what I can find out through the internet, real life, so is climb performance and take-off performance.
The airplanes now follow pretty close the max or optimal altitudes and speed as indicated by the FMS ,before they where way off.
If you really want a freeware airplane that has very good ,lifelike, performances you might consider the aerodesigns A340 package (BTW with an excellent panel and sound package) which also can be married the PSS
's package if you want a functional FMS.