I seem to recollect reading that the C2C (Whitehaven to Sunderland) is largely ridden on tarmac with only a few truly offroad sections .
So my suggestion for upgrades would be a good pair of road/slick tyres - cos you're going to curse those knobbly tyres after a few miles on paved roads
Continental travel contacts are pretty good at road and off road action. Conti Speed kings is a 29er MTB tyre that has a centre slick section, it is light too but limited puncture proection unlike the travel contact. Otherwise you could look at the various conti hydrid tyres like the contact.
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So my suggestion for upgrades would be a good pair of road/slick tyres - cos you're going to curse those knobbly tyres after a few miles on paved roads