Hardly any flight cruises at FL380 immediately after takeoff on an 8-hour flight. Do step climbing. You’ll save a lot of fuel this way.
As for the A333, I think the cruise is around M0.83. The tutorial recommended by @Andre_S should help. I’ve only flown the A333 once so I really don’t have much experience on it.
As for the 777, it is the same idea. Do step climbing. If not you’ll burn a lot of fuel. Ideal cruising speed is M0.84, but a range of M0.81-M0.87 will do, Max M0.89 (if the A/C is really overweight and you need to burn fuel quickly). To give you a rough estimation of the stability, the 777 naturally noses up around 2.5 degrees above the horizon. If it is <2.5degrees, you are fine, but you are flying a little too fast. If the nose rises >2.5 degrees then monitor the flight because it suggests that the autopilot is struggling with trying to gain lift. It can result in a crash if uncontrolled and/or not monitored.
Hope it helps