Hey frosty,
Actually the contrast ratio of boot monitors is actually 1000:1.
The other listed number is more of a marketing scheme type thing. Its called dynamic contrast, which is an "adaptable contrast" the screen will automatically adjust brightness and contrast depending on if its a lighter or darker image on the screen. It's not as cool as it sounds. When you have a bright screen it makes it brighter and more detailed, but a dark screen gets way to dark. Very backwards in my opinion.
The 2493hm has a dynamic contrast of 10,000:1 where as the 2693hm has a dynamic contrast ratio of 3000:1. I personally own the 2693hm and have played with the dynamic contrast but don't like it very much. The real number to look at is the lower one is the lower one which for most monitors these days is 1000:1.
1000:1 is also only achievable at 100% brightness, so in other words I have my brightness at a bright but very comfortable 81, and achieve 477:1 contrast ratio when calibrated correctly.
This is a great all around monitor (I also have had two different fhd2400 Gateways which I returned because they looked great at the store but quickly developed horrible backlight issues) and I am very happy with my decision. This is better in my eye than the Gateways, and although the extra size of the 2693 on paper dose not seem like much, it makes all the difference. I believe it to be the absolutely perfect size ratio for big lcds. It's a magical size, and if you end up getting one, you'll see what I mean.
That all being said, neither are 1080i both do 1080p, so if thats the most important look else where, if it's not a hug issue you may just love these monitors.
I hope some of this helped. Good luck with your next purchase!
P.S. Its always good to buy from a place with a decent return policy, so if even a single dead pixel, or backlight bleed
You can return it quickly and get something that makes you smile