Your Shimano rankings are right. It continues 105 -> ultegra -> Dura Ace.

Most cyclists can't notice a real difference between 105 and up in terms of handling. There's a weight difference, but the shifting is very, very similar and crisp.

Sora is definitely slower the shift than 105+. Plus, it's important to realize that Sora is NOT compatible with 105+ (can't use the same chains/cassettes and swap around), and that Sora also has a 'thumb-shifter' for the RD downshift, which means you can't shift from the drops for most. I will say without hesitation that 105 is a better groupset than Sora, in pretty much all aspects.

However, this does NOT mean that Sora = crap. Sora performs excellently, and in fact, near flawlessly when well adjusted. It also doesn't wear out prematurely, and a good thing is that the parts like chains and cassettes cost half what the 105+ line costs. I'm not a beginner cyclist, and I still ride Sora on my main bike. (My race bike is Dura-Ace, and yes, it's better crisper shifting.) I would venture to say that Sora is more than enough quality for nearly all beginners.

The main situations where I'd say avoid Sora:
1 - You already know you'll hate that thumbshifter downshift. Happens a lot from folks who are already used to 105+. I don't have any issues with the thumbshifter myself, but a lot of folks really don't like it.
2 - You know you'll get upgraditis because all you've been researching is 105 and up. If you feel like Sora is a step down from what you want, don't bother and just get the pricier stuff - you'll invariably find some mental excuse to justify the upgrade even if there's no practical reason to do it. Upgraditis is prevalent in cycling, so buying what you really want up front is the cheapest option.
3 - You'll be racing crits. As trouble free as my Sora is, I would definitely go 105 and up for criterium racing, where fast, hard shifting repeatedly is the norm. The Sora shifter will probably be finicky enough on those shifts that you'll get annoyed during a crit where seconds are crucial for not missing a breakaway.

Last thing - unfortunately, Shimano sells Sora as an on-bike groupset - it's actually hard to buy a replacement Sora groupset unless you go to special dealers online. Shimano wants you to be in the forced upgrade path of 105 up, where they can make good profits. So even if you plan on riding your bike until the group wears out (which I'm currently doing), it's likely that a 105+ upgrade will be in your future.