As others have pointed out, it’s not necessary to do your reviews more than two or three times per day no matter how fast you want to finish. I think @rfindley or someone once did a simulation showing that the difference between doing reviews three times vs. twice per day is pretty negligible, too.
Speed is mostly gated by how fast you do lessons. Do more, go faster (and tax your brain more, risking burnout).
Success is mostly gated by doing all of your available reviews at least once per day, every single day if at all possible. My advice to anyone is to get the pile down to zero at least once every day (or at least as soon as is reasonable after falling off the wagon).
Note that speed and success can be measured in at least three ways:
Progressing through Wanikani levels
Completing all available Wanikani lessons
Successfully memorizing (with “burning” as a proxy) all or most of the items on Wanikani
I am kinda middle of the road, and definitely not a “speedrunner” by any stretch, but I care a lot more about the latter two metrics than the first. It took me almost exactly three years to complete the first two metrics, and I’m still working on the last.
I did my reviews (and lessons) only once per day for the most part (twice per day became more common for me in the higher levels). Twice per day throughout would have made the task harder for me, but it would have gone by quicker.
“Three years” to me seems:
Moderately slow by the first metric (~2.6 weeks/level).
Modestly quick by the second metric (~8.3 lessons/day). Note that I almost never did more than 5 lessons/day early on levels when there was mostly new kanji, and often stopped altogether when I had too many early stage items.
A reasonable pace by my standards for the third metric. I’ve currently burned 6685/9087 items, or ~74%. So far I’ve been burning at a pace of 6685 items in 1154 days, or roughly 5.8 burns/day on average (it’s anything but linear, of course).
Nobody has mentioned them yet, but while I’m a huge fan of dashboard user scripts, and used a few “extra info” scripts during lessons/reviews, I’m slightly suspicious about scripts to reorder lessons or “doubletake” review quizzes. As long as you get the review pile down to zero every day, I don’t think it really matters that much, but, FWIW, I never reordered lessons or “took back” any of my incorrect answers, even silly typos.
To net it out: “plowing through your review pile” is never a bad thing. But “felt like giving up” might be a warning sign.
Just remember that unless you burn something, every review you do today is going to show up again at least once, possibly several times, over the next 120 days. The only ways to make your review load lighter is to:
Slow down on lessons (if you find yourself in a hole: stop digging).
Burn items (removing them from your reviews forever).
Change the “shape” (pareto) of your review queue (more later stage, fewer early stage). Stage 1-4 items (Apprentice) will show up once or twice per day, every other day at best, while stage 8 items (Enlightened) have only a 1/120 chance of showing up on any given day. This is where the advice to keep your apprentice items under ~100 comes from, (FWIW, I liked the “apprentice + guru <= 150” algorithm.)
Note that 1 also makes 2 and 3 easier (it’s easier to memorize fewer items and progress them through the stages more quickly).
Good luck, and don’t give up!