So whats the difference between these two discs? One is 10 quid cheaper..
https://www.chainreactioncycles.com/shimano-xt-rt76-6-bolt-disc-rotor/rp-prod39007
https://www.chainreactioncycles.com/shimano-xt-rt86-ice-tech-rotor/rp-prod67197
RT-76 = floating rotor
Rt-86 = Ice-tech floating rotor. 3 layers with steel sandwiching aluminium. Supposed to handle heat a lot better. If you're a brake dragger they might be worth it, otherwise just get the 76's
In theory the Ice-tech one will dissipate heat slightly better, and make your wallet slightly lighter
"Shimano's XT RT76 6-Bolt Disc Rotor provides ... Precision cut from stainless steel ..."
"Shimano's XT/Saint RT86 Ice-Tech 6-Bolt Disc Rotor ... Featuring a three-layer sandwich construction of stainless steel and alloy 3-layer to rapidly radiate the heat ..."
that's your difference.
Surely the best answer is simply "10".
Not as correct as "RT10", though, unless RT = 1