Thanks for all the input! Responding to some of your questions -- and to let you know where I'm coming from . . .


- There ARE great deals on Ultegra 6800 out there, but there are even better deals on 105 5800. I bought my entire 105 groupset for somewhat less than $400. For 6800, the best deals out there are about $300 more. Since this is my indoor trainer / bad weather / night training bike, it's not going to get Ultegra.


- One thing I don't like about Sora is that front shifting seems a little high effort and long throw. It appears that the lever throw is the same with 105. But maybe there's something to be done about effort. The clearest physical difference among Sora, 105, and Ultegra is the crankset. All three have the 4-bolt arrangement and styling, but the big rings are very different. Looking from the back, the Sora chainring appears to be stamped out of flat metal. There's not much help for the shift to the big ring. The 105 chainring isn't hollow but it has a grid of convex contouring on the back and has more ramping to help the chain up to the big ring. The Ultegra chainring has smooth convex contouring on the back and has even more ramping to help the chain up the ring. Perhaps this is one reason why Ultegra front shifting is better. At any rate, I've got a spare Ultegra 6800 crankset. If I go with 105, I will use the 6800 crankset. (And if I return the $90 105 crankset, that makes the decision to go with 105 even easier.)


- The other thing I don't like about Sora is the larger gaps between cogs in back. There's only one way to fix that -- more cogs. But I've got to decide how big a deal this really is for me on this bike.


My Allez has Axis brakes that are pretty flimsy. I'm going to upgrade the brakes, either way. Assuming that, and assuming that I use the 6800 crankset I already own, the Sora-to-105 upgrade would cost me less than $250.


Thanks for the comments. Any other thoughts?