in Autopilot mode you can speed up to 16 times normal speed (just press R+ 4 times in a row and R- to go back)
At 8 or 16 times normal speed you have no more AI
In manual mode you can speed up to 256 times normal speed.
Xtra tip: when you speed up your sim on an IFR flight you don't want to loose ATC, so best thing to do is respond positive to the command when ATC asks you to take contact with the next ATC post but don't take contact with that ATC command.
will then automatically jump ATC frequency each time you come into another area without you loosing ATC guidance.
Once +/- 150 miles (actually it is your Altitude divided by three---> ex. at FL390 it will start your descend at approximately 130 miles from your destination) from your destination you can recontact ATC, they will probably tell you to do an 180° turn a couple of times in a row but you can disregard that.
After this it'll say that you can maintain your present heading and from then on you have your normal ATC back