I thought it's 30.5 with stand, without stand it's 26lbs or so? I'm considering this mount with a 27" because it's readily available in Canada for a decent price.
Well, no. This has been discussed extensively in this thread. Take a look at post 36 and subsequent ones. The weight of the iMac without the stand is 28lbs. Which would put it under the 30lbs limit.
However.
In order to affix the iMac to the arm, you need to add the special Apple VESA adapter and screws. That's additional weight that needs to be added to the 28lbs. And I'm not clear about the Ergotron MX, but for example in the Ergomart arms, they supply the VESA plate separately (depending on your VESA size), and the weight of that plate and screws again needs to be added to the total weight being handled.
So. That means we are again pushing closer toward the 30lbs. But if we are still slightly under the 30lbs, why is that a problem? See my post 46 in this thread, a discussion with the manufacturers of Ergomart arms, and which applies to all gas cylinder arms. Relevant quote:
"Now, if you mount the iMac, you remove the stand which is 2 lbs 10.2 oz, but you add the Apple VESA adapter, as well as a 100mm VESA adapter at the other end, which again gets you close to the initial weight of a hair over 30lbs. So as can be seen, this is right at the edge of the weight capacity of the 7601-14-2000. An Innovative rep pointed out that all gas cylinders lose potency over time and have to be tightened to keep functioning, and "if you are already at the edge of the capacity, you don't have any room to tighten". And the cylinder in the 7601-14-2000 is the largest cylinder on the market. Other posters have been in communication with Innovative, and Innovative does not recommend the 7601-14-2000 for the 27" iMac."
It doesn't mean that you can't use the Ergotron MX for the 27" iMac, as the weight bearing capacity is still within official specs - all I ever claimed, is that it's right at the edge of those specs. Given that, you have no margin, and possibly you may have shortened use, because as soon as the cylinder capacity diminishes (according to the engineers I spoke to, the cylinders lose potency at about 2% per year), you are right out. If the iMac were only 25lbs, you'd be able to afford a few years of capacity loss from the cylinder. Here, you have none. Potentially, that means your arm will start sagging after about a year.
Now, it may be that there is an additional margin built in to the spec of 30lbs (i.e., in reality the engineers put in a fail margin of a couple pounds more unofficially, to, say, 32lbs), but that's an unknown, and I personally don't want to take the chance, because there are always additional considerations. For example, I have 6 cable connectors hanging from my iMac, with one being pretty hefty (a stereo adapter to heavy duty audio cables) - those cables again add to the weight the arm has to carry. Or this scenario: I frequently hook up my iPTouch 4G to the iMac with a cable to synch and charge. The cable doesn't weigh much at all - but, because of the angle it puts a certain amount of mechanical tension on the arm, as the cable hangs attached to the iPT that's lying on the table. It all adds up. Specs are one thing, but in real life you find that there are a variety of use scenarios which may put unexpected strain on the system - so it's better not to be as close to the spec margin. Again, YMMV.
