It's simple maths for me.
If I do a Harrogate to cockfosters run (about 200 miles for me each way) it takes about 2hr 50 mins each way and I'm at 90 for long stretches.
If I lower my speed to say 70mph its going to take me about another 50 mins
50 mins to me is about £22 lost yet my fuel will be down by maybe £8 I'm guessing.
Plus I want to get the bloody job done and when I'm flying down motorway very few lane changes and messing about so it's actually more stress free.