Main difference for me is the folded length. The non-T folds down to 21.3 inches, while the T folds down to 16.1 inches. Very significant, IMO, if you're looking for a travel size tripod.
At 21 inch's why not go to a series 2? My 2541 is only 22 inch's and I think its more stable? Ben I am sure you know this.
Also Ben, I think you have the right idea having 1 for travel and 1 for ultimate stability. I love the 2541 but I wonder if its to big to take on a trip. Something tells me next time I fly I will want to ad a smaller setup. I have nothing planned for a while and I find the 2541 fine to take around town and a perfect middle ground. I guess for the 5 inch's or so I will just make it work, its really a great setup and while not exactly small its very sleek and almost stylish.
tat's your gonna love the markins head. Night and day to the Manfrotto stuff and really IMO makes a bigger impact then the tripod did. Its just about as easy to frame a shot as it is hand holding the camera.