Cynan -- I figured I'd add my two cents. I've been lurking forever and now I finally have a chance to contribute.
I've ridden both bikes. When I first started searching for a full suspension bike I was looking at the Specialized Stumpjumper and the Specialized Enduro. Both were nice, but I felt like I wanted something in between. I thought the Enduro was too much for my needs -- it's heavy (compared to the Stumpjumper and the ETSX) and has more travel than I needed. As I was about to settle on the Stumpjumper, my local shop got in one ETSX-50 and it was my size. I rode it and never let go.
In my humble opinion, it's the perfect bike. The geometry fits like a glove ... something I didn't find on the Specialized bikes. Of course things may be different with you (read: try both bikes to determine how they fit / feel). I also liked the adjustable travel and flexibility of the ETSX-50. You get 3.5", 4", and 4.5". Add a Talas (or other adjustable) fork and you have a real do-anything bike. I think the thing I like most about the ETSX-50 is that there's no peddle bob. It really is a great all-around bike ... just read the reviews.
Of course all of this is dependent on the terrain you ride. The ETSX-50 does not have as much travel as the Enduro, so it's not necessarilty a fair comparison. If you don't need all of the Enduro's travel, I would give the ETSX some serious consideration. The other thing I'd mention is that the ETSX line uses the same frame, no matter the number (30, 50, or 70) -- only the components change.
Anyway, I hope all this has helped. Good luck with your new bike decision.