parts
 

Pardon my parts ignorance...but: my bike (well, I have two others, but this is the only one I really ride), an Independent Fabrication, si 14 years old. Recently was having lots of shifting problems, including a really strange one: a number of times, the chain came off of the cassette, and got wedged between the wheel and the cassette. A number of trips to LBS (a high quality, very reliable place) didn't fix it, and finally, they decided to replace much of the drive train. Chain and cassette (those, of course, have been replaced many times), one of the chain rings (I have a triple) and the rear derailleur (the front was replaced 2 years ago).
Not it's working much better, but do to availability these days, these are lower grade parts than Ii've usually had, like a 105 cassette instead of ultegra, tiarga chain instead of ultergra, deore instead,...
How much difference do these things make? I really don't' know.
If it's just wieght, for my life, style and purposes, it doesn't much matter.

It sounds like you could do with some tutorials on how to maintain a bicycle. There are so many on YouTube and at websites such as sheldonbrown.com and any listed here: https://www.makeuseof.com/tag/10-onl...riding-skills/ Any time the chain lodges between the wheel and the cassette it is a good sign the inner stop on the rear derailleur has not been set properly, It should never happen. Learning how to do your own simple maintenance will save you money and the time to take it to the shop. This one setting shouldn't take more than a couple of minutes.

I like Shimano Deore for my level of use. It works well, lasts a very long time, and does not break the bank. Once you get above Deore, the improvement in performance is slight but the cost goes up a lot. The "fIts and finishes" go up with the cost and the weight goes down. Not enough to make me want to use all Ultegra.
You can see the lineup for road bikes and mountain bikes here: http://www.chainreactionhub.com/road...ra-to-dura-ace http://www.chainreactionhub.com/mtb/...m-deore-to-xtr

Another thing that can cause a chain to slip between the cassette and the hub: a bent derailleur hanger.

Any rear shifting problem that doesn't respond to cable tension adjustments, the first thing I check is derailleur hanger alignment. Most times, that's the problem.

If the problem has already been fixed, then to the OP's question, the differences between 105 and Ultegra are weight and smoothness, but successive generations have been getting better, so a later generation of 105 might be just as good or better than Ultegra from a previous generation.

None of that matters if it's not adjusted properly. The stop limit screws prevent the chain from falling off the edge of the cassette, assuming no bent derailleur hanger. The cable tension adjustment and shifters control the shifting in between those stops.

If they make no difference that you can tell, then they make no difference at all.

Minimal difference. Ride more, worry less.

How thinly can you slice the baloney. Shimano, for example, makes so many grades of road bike components that I can't keep track of them all.

As you move up the cost food chain, the components really do get progressively nicer. They are lighter in weight, they function more crisply and they look better. The lower lever offerings still work, just not as nicely. The Shimano marketing people have been tasked with making sure that, however much you are willing to pay for a derailleur, they will have a product on offer that will consume that entire budget. They have done that job quite well.

I've been rding for over 20 years. Until now, I never had a chain go between the cassette and the wheel (I've had chains flop off of the front once in a while, but that seems to be the price of having a triple chain wheel. The innter stop was set multiple times at my LBS. People can think whatever they like,but I'm really not interested in working on that stuff...I've got too many other things gonig.I let the bike store deal with it.