On a ride last night with a guy riding in a set of the EA90 SLX and a spoke pulled out if the rim! This was on a front wheel and he is less than 70kg. Not sure if this is a one off deal or if the wheels were over tensioned. Read the reviews to get a real sense of these wheels. I would recommend looking into the HED C2 line of wheels. Lighter, less expensive and has a 23mm wide rim that does improve road feel.
If you want a really good set of wheels consider getting a custom built set. You will get exactly what you want and it will not cost more that a factory set of wheels.
My wife rides on a set and is very happy with them so far, but hasn't done many km yet and only weighs 50kg. They roll extremely well, arrived perfectly round & true (and are still that way some 500km later on dodgy Australian roads), and in the short test ride I did on them seemed to be quite stiff and transfer power well (I weigh 78kg).
In terms of 'feel' they handle better than the Ksyrium elites that came on her bike, she corners noticeably faster.
What don't I like? The alloy freehub is a pain with an Ultegra 6600 cassette, very tight tolerance and if you don't align everything perfectly before you crank down on the lockring the machining on the inside flange of the freehub can bite into the alloy carrier of the cassette. First time I fitted a cassette to this hub the result was that the cassette wasn't completely perpendicular to the axle, with a wobble of a couple of mm side-side in the big cog as the wheel rotates. Only remedy was to use a new cassette, and take more care in fitting (luckily I was able to swap her cassette to my bike and it was fine on my DA freehub). The near-new 6600 cassette that came off my bike was equally tricky to fit, but went on OK in the end so it can be made to work. A 6700 works better (she has switched to a compact crank and needed different ratios), haven't tried SRAM or other Shimano cassettes so YMMV.
I'm running Dura-Ace 7850CL on my bike and these are a reasonable alternative to the EA90SLX. Similar price and weight, but feel like maybe slightly less weight at the rim. They don't spin quite as well (don't have the ceramic bearings of the R4SL hubs) and the rims are probably less aero, but they seem a little more robust and the freehub is certaily less finicky about cassettes (any 10spd shimano/SRAM works). These seem to get excellent reviews, and IMO they handle really nicely and are very comfortable while still being stiff enough that I never get any brake rub when sprinting out of the saddle (mind you I'm not a sprinter so YMMV).
Thanks for the replies. I have seen enough reviews saying spoke durability can be a bit of an issue, aswell as the cassette chewing up the freehub body. I am curious as I have seen a deal online for brand new wheels for US $400.
Significantly lighter than my cosmos wheels but not sure if worth the durability question or how much of an actual upgrade this may be.