Modern Arm chips will maintain a wide gap in performance for quite awhile.* Arm has poured a lot of money into optimizing their chip IP and it speaks for itself in the benchmarks. Excluding if performance wasn't a concern to begin with - I don't see the argument why an open ISA is really worth the performance / heat / power cost.
I hope you realize that you're talking about a cheap SoC that was released in late 2022, and does not reflect currently announced RISC-V microarchitectures.
e.g. SiFive P870 is competitive with ARM's best, whereas Ventana Veyron V2 and Tenstorrent Ascalon/Alastor compete with the state of the art from AMD/Intel/Apple/Qualcomm.
According to SiFive, the P870 is roughly equivalent to an ARM X2 or AMD Xen 4, so it's about two or three generations back from the Cortex X925.
I've yet to see a catalog part w/ that core, but the guys I know at SiFive say they're pretty sure it should hit 3GHz, which is cortex X2 territory. Not exactly ARM's current best, but they're definitely closing the gap.
One difficulty in evaluating SiFive's cores is their business model is to license their designs to companies who are fabbing their own custom or semi-custom SoCs, so they don't appear in generally available parts until much later.
Or even anything better than an A76, announced May 2018? (Pi 5, Rock 5, etc) Which implements ARMv8.2-A from 2016.
Yes, I know ARMv9 cores are available in high end phones running Android. But not, that I know of, in SBCs or laptops running Linux.
We've got several different RVA22+Vector (latest spec, ratified March 2023) RISC-V cores, SoCs, SBCs and laptops on sale right now, with much faster ones (P670, A78-class) coming around the end of the year.
That requires actual hardware, which naturally tends to be in mass production (i.e. cheap) SBCs around four years after the announcement of the core. That's a constant over Arm and RISC-V e.g. we've just in the last two years seen Rock 5, Pi 5 (nine months ago), Orange Pi 5 with Arm A76 cores announced in 2018.
P870 was announced in October. It'll be a while!
P670 was announced November 2022, and will be in e.g. the SG2380 around the end of this year -- actually remarkably fast. It should leapfrog those A76 boards in performance.
If you don't have the actual hardware, discussion about performance is a waste of time. If you disagree, I urge you to invest in my chip startup. Our chips get 10000x better performance than the any other RISC-V chip on the market. The hardware itself won't be out for 100 years, but that doesn't matter to you :)
*: https://www.phoronix.com/review/visionfive2-riscv-benchmarks