Journey times
Assuming everything legal . . .
Max speed no trailer = 70mph
Max speed with trailer = 60mph
You need to add appx 15% to your journey time.
However, as noted, getting too and from those speeds takes longer with a heavier vehicle and 'live load' so I'd add about 20% to any motorway based journey, and probably around 25 - 30% to any other.
Remember also that with a trailer and live load you will lose much of the abilty to 'lane hop' and will spend more time in lane 1 doing 56 behind the lorries - an extremely sensible option in my view.