Giant anthem x4 26er for single track
By looking at the current frame geometry at http://www.giant-bicycles.com/en-gb/bikes/model/anthem.x4/7865/45505/#geometry we can assume the following.

Descending:


HA: 71 degrees head angle is pretty steep for downhill but for flowy singetracks it will be good. For the "steepish rocky tracks" it really depends on what you consider steep. Anything more than 10% and at over 15km/h may feel uncomfortable on the 71 degrees HA.
cockpit: You can improve the descending characteristics of the bike by using a shorter stem and wider bars.
travel: The 4 inch front and rear travel will not be enough for the very rough stuff.
verdict: So if you are very interested in aggressive MTB trail riding then this bike will not be appropriate. If you are just starting out then it'll be OK.


Climbing:


HA &amp; SA: The 71 HA and the 73 seat angle make for a great climber.
travel: The 4 inch front and rear travel make a great XC bike and will allow you to easily tackle long epic rides on the mountains (for example 30 to 80km rides). Increasing suspension usually reduces this number.
verdict: Really good climber especially if it'll come with good (light) wheels and appropriate tyres.