Gary Whitfield

Yes, they (probably) work on them in more-or-less chronological order but there are a lot of factors that can make some a little faster than others, and some a little slower than others. This is the reason that USCIS gives a "goal time" of 5 months, but in reality has been doing them much faster-- they don't want to field calls like this all the time, and they would if they gave more accurate data. The VJ data is also really just a guide-- you can't predict if you'll be on the faster end of the average or the slower end of the average. And while YES it stinks to be on the slower end of the average, you're looking at a difference of maybe 2 or 3 weeks within a service center, not a difference in months between service centers (which has happened before and which advocates from right here at VJ made STOP happening).
Imagine that the Lockbox boxes up petitions as they come in, and then ships the boxes off to CSC. They'll be in rough chronological order (not perfect but close). Jim, Bob and Sue all work at CSC. They open a few boxes, and Jim takes Feb 1 through Feb 3, Bob gets Feb 4 and half of Feb 6, Sue gets the second half of Feb 6-8. They all start working at the same time. Sue's second half of Feb 6 gets done on the same day as Jim's Feb 1 and Bob's Feb 4. Then, imagine that Sue us faster than the other guys naturally, and Bob got unlucky with a really bad batch of handwritten applications. Jim's kid got pinkeye this week so he had to stay home two days, and Bob's been putting in 10 hour days because he's taking next week off because his daughter is getting married in Hawaii. ALL of this will break any sort of strict chronological order, but it will still be more-or-less at the same(ish) time-- within a week or two.
Then add in the applications themselves. Some ARE more complicated than others, or have more things to check. I have LONG thought, and have little proof except for anecdotes, that applicants who HAVE traveled to the US before take slightly longer than those who have not. Seems strange at first until you realize that they probably check with CPB to take a look at entries/exists looking for any funny business. That, for all we know, could be an official request they need to put in and it could be dependent on CPB's workload, too-- sometimes they get it back next-day, sometimes CBP has a week or so backlog. This, again, is a total guess based off of years working for/with the government-- I wouldn't be surprised if I'm right but could easily be wrong.
Either way, you know almost for sure that you will have your NOA2 much quicker than USCIS's 5 month goal, and honestly I'd personally bet this week. You can go ahead and call but I really don't recommend it. There's a 50/50 chance they'll give you the wrong information that will enrage or confuse you and there is *nothing* they can do for you away. You could apply for an expedite but you are extremely unlikely to get one (job or no job-- they've turned down people with life-threatening illnesses and pregnancies etc) but even that takes a few weeks and you're all but guaranteed to hear this week anyway.
Get your hands on the checklist for your embassy, start gathering everything you need for embassy stage now (this could save weeks!) see if you can arrange your medicals now (could also save weeks!). Instead of trying to move something that seriously just won't move, get yourself ready to jump into action the moment they DO move-- that's the part you have control over-- how quickly you can knock out the embassy checklist!

Please understand that VJ's estimates have nothing to do with the official USCIS processing time. VJ's timeline estimate revolves around having it's users put in correct data, which is frequently not done. No matter what your timeline estimate says, it matters very little -- the USCIS processing time is 5 months standard, and as such you are within that waiting period. Calling them will not help. Arguing with them will not help. You can literally do nothing until your 5 month wait is up.
Last year a lot of us watched as our VJ timeline estimate surpassed our wait time. Then we watched as it surpassed the USCIS processing time. Then, we waited as it surpassed their excuses. Then, maybe 300+ days later, people felt like touching files. Your wait won't be as long as this. Usually a few months for CSC, maybe a little longer due to the fact that CSC is the sole processor of K1 cases now.
Think of it like this.... your application most likely goes into a giant bin. It might be on the top or it might be on the bottom depending on where it gets dumped with thousands of other cases. Maybe the immigrant officer will pick it up, maybe they won't. Maybe they'll have your case in a stack of other cases on their desk, maybe they don't. Maybe they picked it up, but then got distracted playing Candy Crush. Or maybe their office looks a little like a disorganized mess from hell.
Your country of origin has nothing to do with it. Your risk factor has nothing to do with it. The USCIS barely looks at your file. It goes through a checklist process to see if you've done everything correctly, including I assume if you have have been okay'd on background checks. Their handling of your file literally takes somewhere between 10-20 minutes so I've read, before they move on to the next.
Once you get out of the USCIS part of things, provided the USCIS passes your case file over to the NVC in a timely manner (sometimes they are not prompt to do this at CSC), then your country of origin and risk factor (as judged during the interview) comes into play for the embassy process. London is an easy consulate to deal with.