Although no longer available from the pull-down menus, using the key combination [ALT]+[T] will double your ground speed, effectively relieving the tedium of a long flight.
[ALT]+[T] again will quadruple your ground speed,
[ALT]+[T] again will increase your ground speed 8x,
[ALT]+[T] again will increase your ground speed 16x,
[ALT]+[T] again will bring your speed back to normal (1x)
Did you know, however, that if you open the instructor station (press [I] or click “Show IOS” from the Flight pull-down menu), there is an analog(ue) ground speed slider. This slider allows you to reduce or increase ground speed without having to cycle through the higher speed levels to get back to 1x. It only goes as high as 6x but you can set any speed you like between 0x and 6x. It is particularly useful if you want to slow your ground speed below 1x or increase ground speed only slightly like 1.5x