I think you’re both right, though Simon’s phrasing of the point might have been a little more extreme than the words I’d pick.
My records show me that memorisation quality is inversely proportional to memorisation speed and directly proportional to recall speed.
You’re going to get better by taking this “17” approach that you’re taking, but assuming you already know your images well (mere exposure will not improve your time much like it would in the very early phases), but you’re not going to get faster until you attempt to go faster, and fail or not, you’ll gain that skill by sleeping on it.
You are going to have the tools to do an above-average job of making decent imagery when going faster, but still, that is the necessary step.
Small groups are great for improving your speed as well when dedicated to that end. You can do a pretty bad job and still get good feedback, whereas if you did so poorly (sloppy) with a full deck, there’d be too many errors to be of use. You couldn’t learn anything from them. But with a small packet you can go at very high speed, check out the results, and then back off the speed a little at a time and exercise more care and finer technique until you’re at that top speed that still allows you to get 100% sometimes and huge holes rarely or never.
Your speed with 52 cards is going to have to be slower than this, but you’ll be able to find the right speed by backing off some more when adding the rest of the cards. It’ll be a speed well within your comfort zone since you have already been moving more quickly.
Something I’ve been doing recently in my training in various areas when it looks like this is adding the smallest reasonable quantity, which will probably be one locus per day as long as my performance doesn’t plummet, which is a rare thing since the addition is so small. In other words I do this as a rule rather than basing it on my performance, that I have to be “this good” before adding more. I just assume I’ll become “that good” along the way, and add little by little from the start.
May or may not be your style, may or may not work for you here, but I recommend taking this road over adding large chunks at certain benchmarks. By “one locus per day” of course that could mean “one locus every other day,” just depending on what time frame you have in mind to get to the full 52 cards.