Another thing to add regarding pro XC racing: Never take what pro XC racers use as the final word of what is fastest. Pro XC racing has been late to nearly every party in terms of MTB progression. Examples include....
-Dropper posts
-Slacker Head angles
-Ditching narrow bars, long stems, and bar ends in favor of wide bars and shorter stems
-Full suspension
-Larger volume tires.
After years of poo-pooing these things, all of these are now found on the pro circuit.