What do you weight? Are you hard on parts or a smooth rider? Hardtail or full suspension? Tubeless? Centrelock discs or 6 bolt? What wheels do you currently have?
For $600 I would look for either of the following:
Shimano XT
$550
~1650g
Tubeless
Cup and cone bearings
24 spokes
Centrelock
http://chainreactioncycles.com/Models.aspx?ModelID=20794
Custom XTR Hubs with Mavic 717 Disc rims
$550
~1550g
Not tubeless (require rim strips for tubeless setup)
Cup and cone bearings
Full 32 spokes
Centrelock
http://chainreactioncycles.com/Kits.aspx?ModelID=2579
Custom Hope Pro 2 with Mavic 717 Disc rims
$450
~1650g
Not tubeless (require rim strips for tubeless setup)
Cartridge bearings
Full 32 spokes
Very loud freehub
6 Bolt disc
http://chainreactioncycles.com/Kits.aspx?ModelID=7599
In terms of performance I think all these wheels would be a fantastic upgrade. I would probably go the custom route if I was buying new wheels at the moment, they are far easier and cheaper in terms of finding replacement parts. That being said, the XT wheels are a very tidy package that are pretty hard to argue with for the price.
I don't know much about Easton wheels really, but DT Swiss make fantastic hubs, though a little pricey. I am not really a fan of DT Swiss rims, I found them to be a little soft compared with the Mavic alternative. That being said, some people have very good luck with them and rave about their quality.
There are several specific wheel threads in the XC part of the forum that you might find useful before you make your decision. Good luck