If you own one camera then the a65/77 can do anything you can imagine. But if you own already a65/77 & a850/900 then i separate the purpose for each camera. The a77 is my easy shooting,sports,birds etc and if i want landscape,portrait etc then a900 is in use.
The same is with Canon. If you want sports,bird in fly etc then you go for the 7D.
If you shoot landscape,portrait etc then 5D is the way to go.
The same is with Nikon D300 and FF D700 and the upcoming FF D800 with the D400.
If you can wait until February before you go and buy the A850 it will come out the new a99 at the range of Nikon D800 and Canon 5D III. It is up to you the decision, good luck.