Updating this with initial impressions.
I ended up mounting a 29×2.35 MM and a 27.5×2.35 HD both on soft.
Measuring them up them came within 1mm of the old Spec 2.6″ tyres. Overall they are lighter and roll much better.
First ride out I wasn’t 100% comfortable as I had the pressures up a little higher than in the spec. Lowered them on the next 2 rides and I can’t be happier with the results. I’m glad I stuck with ‘normal’ width tyres in this instance. I have since PRd several climbs and downhill sections locally so the ‘narrower’ tyres don’t seem to have had a negative affect.