alright for those playing along at home I had a play with the cranks last night. I have found despite the cranks having a chainline of around 47mm it's still too far down the cassette. hopefully some 2mm spacers may change this, but despite having a ton of room between the chainstay and the front ring, I only have around 9mm of room between chain and tyre, without counting for deflection so its all a bit tight.
This is the chainline with the Raceface cranks and 32t nw ring
SLX cranks chain line, could probably move up a gear
The SLX crankset with snail NW ring I want to use