IMO by the time 105 is worn out, Ultegra is nicely worn in. My BB was just perfect at 25-30K miles. Rear mech, chainset, were fine. I bought my lookalike pedals in 1988 and was racing on them this week. The only crap bit is the headset. Shimano do not do good headsets. Everything else is excellent. The hubs are still doing fine on my winter bike. I built the wheels in 1992. Lock nuts are a bit rusty now, and I did change the freehub for a hyperglide one.
I've got my eye on a new chainset for the race bike, it will be an Ultegra Hollowtech II. New race bike will be Ultegra if I can find the money. And I expect it to last for many, many tens of thousands of miles.