Ok, got a race in a few weeks, across scotland, its over 2 days with day one being 46 miles (road) and 2nd day 18miles off road and 18 miles on road.

My current set up is 29er with Cont race king set up tubeless, but was thinking about getting some slicks with tubes and then on the second day change over to the race kings with tubes. what are peoples thoughts?

Will the slicks make a big different ?

Maybe go for some ‘cross tyres with a fairly slick centre tread but with knobbly sides. 35mm or similar?

how off road is off road?

Depends on weather, race kings are slick for off road anyway, if dry then I’d just keep them on and adjust tyre pressures.

It’s more fire roads, and some singletrack not too muddy

You could try something like a Marathon Mondial.