Yeap, this ^^
Always keep throttle to 100% and drop it to 75% when you reach the 7s mark
Supercruise speed depends on nearby gravity wells, so if there is a planet between you and your destination, try an arc trajectory that will avoid that object
But ultimately it's the distance
For me, to do regular runs (like missions) anything under 1,000 LS is acceptable. While for occasional runs up to 15,000 LS are ok-ish
150,000 LS can mean 10-15 minutes depending on gravity wells within the system
And when you do missions, always check carefully the mission details, more specifically the distances. If it's written 246,845.50 LS, IT Actually is 246000 LS and not 246 LS

Also if a courier mission is paying a million or 2 millions credits - really check the distance - you might have to travel 1,000,000 LS to the destination