what kind of power can an XF driveline take

the drive shaft is a 3" steel with spicer components, would handle up to around 1000nm of torque. alot more than the car can produce. not sure on how strong the trans and diff are tho.

clutch.... pretty pissweak in standard form
4 speed single rail: reasonably tough, will handle a 351 if treated with a bit of respect
Early 5 speed..... 'nuff said that it was also fitted to sigma's
late 5 speed (T5) tuff enuf for most work, dont expect a stock T5 to handle a thrashing once you have a decent engine
BW35&40 series 3 speed auto's..... ok for most driving..... if you drive like a lunatic, they'll die quickly, and neutral dumps (rev in neutral then pull into gear.....) are a quick way to grenade the box

tailshaft is ok, uni's are reasonable, but big power/torque will snap uni's and/or pretzel the tailshaft

diff...... som are ok, some arent.... the Borg-Warner in XF's is basically identical to the one in all later model solid rear axle falcons, and if prepared well, can take a flogging......