You will notice the difference of 800:1 and 3000:1 on the contrast ratio. Alone you might not see it too much but the LG would be brighter esp in the all white or all black screens which is pretty nice.
Basically, you are saying that the Dell is 800x brighter than black and the LG is 3000x brighter than black.
The refresh rate tho you wont notice unless using your computer normally or watching most movies.
Personally, I would fork over the extra 30 and get the LG unless, like Dr.Stevil said, you are looking for HDMI