Well, even A12 and A10X feel about the same to me, yet the single-core AND multi-core is significantly higher on A12 than A10X. Diminishing returns I guess.
I've tested the Air 3 10.5", Pro 10.5", and Pro 11" all side by side together at the same time and they all feel fast to me, with the Pro 11" just feeling a shade faster at times. That's why I said any multi-core score over about 2000 in Geekbench 5 is fast.
View attachment 884281
In contrast, iPad Pro 10.5 A10X does feel faster than iPad 6 A10 even in Safari, despite the fact that the single-core is very similar. The A10 is definitely decent, and in fact I just ordered an iPad 7 with A10 for my wife, but A10X is just better.
View attachment 884280
I'd say it is somewhere in between. Web browsing is NOT just a single-core experience, because more than one thing can be done at a time. It's not as if we're just rendering one window of plain HTML or something.
Similarly, iPad Air 2 (A8X) feels noticeably faster than iPad mini 4 (A8), but their single-core scores are almost identical. However, I didn't actually say iPad Air 2 was fast. I just said it was adequate, along with any machine with a multi-core score over 1000. Actually A8 is OK but A8X is just better.
BTW, for my Windows 10 desktop, I went from an Athlon II X3 435 triple-core 2.9 GHz CPU to a Phenom II X6 1055T hex-core 2.8 GHz CPU, and just about everything including surfing is noticeably faster. Single core performance would be very similar, and thus it's not surprising multi-core PassMark is almost exactly doubled. Everything else in the hardware is exactly the same. Exactly, as in all I did was swap out the CPU in that machine. Initially I was considering buying a new desktop even though all I did on that machine was light business apps, VPN for light business apps, surfing, email, and occasional Netflix, because the Athlon II X3 435 was getting long in the tooth. However, now that I have the Phenom II X6 1055T in there, I no longer desire an upgrade at all, despite the fact this machine is almost 10 years old. I suspect I can use this for another several years. Best US$59 upgrade ever.
Phenom II X6 1055 scores ~400 in Geekbench 5 single-core, but ~1900 in multi-core.