Something is odd here, the Core 2 Duo only has up to SSE 4.1, while the RVA23 instruction set is analogous to x64-v3. I find it hard to believe that the SpacemiT K3 matched a Core 2 duo single core score while leveraging those new instructions.

To wit the Geekbench 6.5.0 RISC-V preview has 3 files, 'geekbench6', 'geekbench_riscv64', and 'geekbench_rv64gcv', which are presumably the executables for the benchmark in addition to their supported instruction sets. This makes the score an unreliable narrator of performance, as someone could have run the other benchmarks and the posted score would not be genuine. And that's on top of a perennial remark that even the benchmark(s) could just not be optimized for RISC-V.

If it's anything like the k1, I wouldn't be surprised if Core 2 performance was on the table. The released specs are are ~Sandybridge-Haswell like, but those were architectures made by (at the time) the top CPU manufacturer and were carefully balanced architectures to maximize performance while minimizing transistors. SpaceMIT is playing on easy mode (they are making a chip on a ~2-4x smaller process node and aren't pioneering bleeding edge techniques), but balancing an out of order CPU is still tough, and it's totally possible to lose 50% of theoretical ipc if you don't have the memory bandwith, cache hierarchy, scheuling etc.