I just finished the Mt Tamalpais century, with 8,200' of climbing and am very thankful that I went with the low gears. I suggest you do the same. Weight is less important than gearing IMHO.
What is it about the McLean that gives you sore shoulders? It should be straightforward to compare the bike fit for the two bikes and adjust the McLean to be more like the LeMond. Start with the BB center, figure out vertically and horizontally where your saddle is fore-aft with respect to that, then ditto for the handlebars relative to the saddle. Perhaps you need to move the saddle back and/or get a shorter stem to reduce the weight on your hands (which is a common reason for sore shoulders).