The 10x50 Swarovski El is an absolutely stunning piece of glass but heavy. I bought the Swaro 8.5X42 EL because it was a little smaller and lighter, and just possibly a bit better in low light. It was hard to tell about the shadow performance in the store, but when the light was good the 10x50 was incredible, maybe a bit better than the 8.5x42 because the image was bigger.
For my purposes, hunting whitetails until the last moment of legal light, general birding, and wearing them in a harness all the time, the 8.5x42 was a better choice. It was a tough decision though and at times I wish I had the fabulous view of the 10x50s.