XC and trails vary and the set-ups associated with them. Here in Colorado the folllowing setup has been killer for me. I ride between 6,000' and 12,000'.
2006 Banshee
Roll Design, Lobo 2 XC package
Axis Shocks
Herman stem w/ 1-1/8 clamp
5 gallon tank
Twist throttle
AC Pro Peg nerfs
RPM front hubs
Douglas Billet Shamrocks
ITP XCs
Stock bore and stroke
Milled head
V-Force 3s
Trinity 2-1 (port matchd to the reed cages)
33mm carb
stock air box
K&N filter and air box lid
PT mids
Toomey silencers w/ spark arrestors (we fabed these up to fit the PT mids)
Evans coolant
Pump gas - Yamalube 2R
160lb jockey
A 50 mile loop is common for us and the pace is really fast for the entire ride. I cant imagine trying to run my modded motor in my XC set-up. I have never needed more motor for the trails we ride.
Good luck with your build.