X bike
With X bikes finishing in 2nd and 5th place in Paris Roubaix, you can bet that they were set up same as the riders road bike.
Normally you use a stem either 1/2 or 1 cm shorter than your road bike and move the saddle back the same amount,
I would use the same size frame as the actual frame design takes account for softer angles and a longer wheel base so its more comfortable to ride.
Raising the bars can help as you do not want to be as low down like a road bike..
