I have a Yukon and am very happy with it. It gets used for just about all my road riding, including sportives, audaxes, long tours (150-200 miles per day), training and club runs. I can keep up with the guys on £5k carbon roadsters so it is capable of speed!
Looking at the current prices, I can't really see how the Etape can be worth £1k more than I paid for the Yukon last year - then again I haven't tried it. All I would say is the Yukon is a fine bike at a very reasonable price for ti.
EDIT: Actually, I've just checked the current price of the Yukon and it's gone up a massive 30% since I bought last year ( :!: ), so the price difference is now only a coupe of hundred quid.
Does the Etape use long-drop brakes?
Is it bit of a squeeze for the mudguards?