I agree with programmergeek. Unless you are ripping the 2x4 (and if so the it likely won't fit on the MFT anyway), you'll be better off using any 8/10/12" chop saw to do the crosscuts on the 2x4s. For the small number of cuts like this that most people do, the weight penalty of the 75 will more than outweigh the advantage of the cut depth. Sears has 3 different chop saws for less than the cost difference of the 55 to the 75. I'm guessing that for cutting 2x4s, a precision saw is not of paramount importance...
I own the 55 and am glad it's no heavier than it is. From the many times this has been discussed, I think the majority agrees with me.