I don’t think weight affects cruise speeds a whole lot, as I understand.

At least, not enough to make your flight measurably shorter.

https://aviation.stackexchange.com/questions/47369/how-is-th...

No, the limit of airplane speed is the speed of sound, as you get very close to that aerodynamics changes greatly. While you can make a plane go faster it is rarely done.

So will an airplane with 5% less luggage or fuel. Go figure.