Don't really know where you're going to find some EA-90's for less than $600usd. I've always seem them ~$700+ for the set, whether it be the sl's, slx's or Aero's.
I really only know about the Eastons, so I'll shed some light for you. Eastons use their own spokes similar to mavic. If you didn't mind having to order a spoke and waiting for it when you busted one like with mavic, it shouldn't be a problem, but Easton uses their own "system" for tensioning their wheels, and thus special tools and spokes must be used to repair the wheels.
For the EA-90's, SLX is the lightweight one, and is actually lighter than the Ksyerium SL's, SL's are made with more spokes and thus stronger than the SLX's, and of course, more weight, but still a light weight wheel. Aero's have the same number of spokes as the SLX, and just have an extra ~10mm of dish to the rim for the aero factor. They weigh about the same as the SL's. If you're a heavy guy or can mash like nobody's tomorrow, skip the slx's, you'll blow too many spokes. Otherwise, all wheels are hand built and you can't go wrong.
Check out Velocity Helios or I can build you similar wheels with Shimano Dura Ace hubs that are more serviceable.
How much you weigh and what type of riding you do makes a difference.
If you use or prefer Campagnolo compatibility that makes a huge difference.