As a present owner of a Rocky Mountain Vertex 990, that has come off a Giant Anthem X, comparing the two is easy the Vertex is a pure race bike it but has all the talked up advantages of the 29er verses a 26'' plus it has the stiffness that will have you thinking how did I get around on a bike that had s much flex laterally! With all honesty the AMB review was pretty much spot on in all aspects, the Vertex is a rocket ship, is laterally stiff but has the compliancy vertically of a smaller travel bike, saying its comparable to a 4'' dually would be incorrect because no hard tail can absorb the bigger bumps of a full travel bike, but small ripple bumps in a trail are absorbed. Where the vertex gets most of its rear end compliance is from the use of a 27.2mm seatpost, not so much the rear triangles construction. The use of the oversized axles, large BB and bloc front fork turns this bike into no other when sprinting out of the saddle or blasting down fire road sections in a race environment.
Now the bad news there aren't any left in stock in Australia, they got gobbled up real quick once released and the only stock left would be what shops have on hand, good news is there is am 20'' size in the Vertex 970 still available from the distributor
http://adventurebramds.com.au. It still is running the same frame as the 990 with a lesser component spec check out the Rocky Mountain page to compare
http://bikes.com. Alternatively bikes can be specially ordered in from Canada, through your local Rocky retailer, it will just take a bit more time but believe me its worth the wait!.
Disclaimer I get looked after by Adventure Brands (Rocky Mountain Aust distributor) and iRide Bikes but don't work for them!
quiggs