The Ultegra version of the 11-speed cassette I want (11-34T) is identical in gearing to a 105 option. It is about $25 more. I wear through these faster than I care to think about. Apart from a (trivial) weight difference, is there any significant difference between the two options?

I have used both 105 and Ultegra cassettes, 10 speed not 11, on the same bike with 2 different bikes. I really do not notice that one performs better than the other. I have done that with 9 speed cassettes also and, in my opinion, the Ultegra shifts a bit faster and smoother than the 105. That could be that the 105 was a fairly well used, but in good condition, cassette and the Ultegra was new. Don't know it that helps with your 11 speed question, just putting it out there.

I think weight is about it, maybe the finish? Neither has a composite carrier for any of the cogs.

I don't know about the 105, but the Ultegra HG800 11-34 11 speed cassette has many of the larger cogs on spiders with solid splines. So it will help prevent your freehub from getting notched up, especially if you have an aluminum one. I've got two of them, one of which is on a DT Swiss alloy freehub. If you take the cassette off you can see the hub splines are clean up until the smallest 3 or 4 cogs, where you can see little notches starting to form (this is after like 3-4K miles, so plenty of life left on this freehub). Like I said, I don't know if the 105 has the same thing.

Fun fact: The Ultegra cassette works great on 10-speed freehubs. That's because the 34t cog is large enough that it can use the MTB trick of letting the big cog sit inboard a little ways without running into the spokes. For all I know it might just be a rebadged XT cassette. You need a spacer (I think it's included) to run it on a true 11 speed freehub.

Edit: Here's a picture of the cog carriers on the cassette (it's the second picture, which doesn't display by default, so you have to click on the thumbnail to bring it up). This vendor also sells the 105 version, but there's no photo from the backside so it's unclear how it's assembled.

https://www.competitivecyclist.com/s...hg800-cassette

The 105 and Ultegra are identical in this regard.

I have two sets of wheels for my current road bike, one has an Ultegra (8000) 11-30 cassette and the other has a 105 (7000) 11-30 cassette. NO WAY I can tell them apart. But I actually think the 105 is ever so slightly quieter.

Weight is the only difference. They are both forged with the same tooth shaping and steel quality. This is a great place to save a little money.

The differences are there. Metal spacers vs plastic, more carriers for the larger cogs, better finish, save a few gram. Typical Shimano. Youll see the same MO comparing other 105 vs Ultegra parts. - Lots of litte differences. Its for the customer to decide if its woth the asking price.

wgscott - I have an extra Ultegra CS-HG800 11-Speed 11-34, brand new, never been installed. PM me if you are if you would be interested.

I was going to install it on my Defy but ended up just trading the bike in and my new Domane came with an 11-34 so it is just sitting in the my parts box in the garage.

Started with a Shimano 6800 11-25 cassette. It was fine.
Replaced with a SRAM 1170 11-28 cassette. It was fine.
Replaced that with a Microshift 11-28 cassette. It's fine.

This is all 11-speed, and honestly, they all shift exactly the same. The difference is the Microshift is 35 bucks.

I've never really perceived a difference in shifting on any cassette, in 10 or 11 speed. Back on 10 speed, I loved the Shimano XT-M771 11-32 cassettes. Cheap, durable, shifted great.

My wife's bike is a Ultegra/105 mashup. 105 cassette all the way.

Weight. Primarily in your wallet.

I believe I'm running a humble Tiagra cassette with my 10-spd 105 RD and shifters. It runs perfectly fine.