I have both and can't tell a bit of difference on the bike. I have
heard the LX occasionally comes too dry and too tight from the
factory. So I loosen the cones and apply more grease and adjust just
right. LX and XT are both quality hubs that will last forever, if
maintained. Only you can decide if the $50 is worth it.
From a business point of view, it is important to have several price
points so customers' varying desires can be tapped. If you want the
very best, whether that is lighter, shinier, smoother, or just gives
you a status boost (at least in your own mind), there is a Shimano
product for you. If you are looking for the best value, there is a
product for you too. I think the LX line fall in the latter category.
When I am riding for time up my local hill (4 miles/1500 feet
vertical), and am at maximum desired pain threshold, I don't give a
rat's patootie if my hubs are a bit lighter, and I know that such
details have no effect on my ride enjoyment or quality. For me that is
the litmus test.
Now answer me this: a whole season of rides up my hill on a Rivendell
custom, or occasionally, my 1986 Dave Moulton made Fuso produced best
rides within 30 seconds of each other, regardless of bike. In
September, I got the bug and bought a Legolas frame. I traded out the
Fuso parts except for required new stem, threadless headset, and canti
brakes. First ride up my hill on the Legolas, I take 2 minutes off my
best time for this season. The weight is close to the Fuso build. So
am I planing? Psychologically enhanced? I love the feel of the
Legolas. In fact, buy the LX hubs and save your $50 for a new Legolas
or Roadeo, or flowers for the one you love.