Differences in DME's

In trying to create a recipe for an Imperial Stout, I am trying to figure out the subtle differences between Extra Light DME and Light DME. The recipe currently calls for a lot of DME, and I was wondering if the Extra Light DME will provide better attenuation than the Light DME. I figured that the hops and specialty malts will provide plenty of body for the beer, and the effects on color between Light and Extra Light will be negligible in that much of a beer. I would rather use the Extra Light DME if it will attenuate better as to keep the beer from being too heavy.

Depends on the brand. But my guess is that extra light is made from Pilsner malt and normal light is from two row. For a stout go with the normal light. If you are worried about attenuation be sure to have good pitching rates, oxygen, temp control. If you can't do that on the cold side another option would be to replace about 5% of your DME with table sugar which will ferment more than DME....