"I can do 1 or 2 pullups, and then I have to go lie down for a bit..."
That's too funny radar2011; I usually feel the same way, and I only weigh 125. Guess that goes to show you that it's more about strength than body weight. I'm very impressed.

As for the lat bar/pullup equivalency, I"m pretty sure it's harder to do a pulldown than a pullup, because I can only do ~90 pounds on the lat bar, but can move my body weight for several reps now the other way. Not sure why.