I had the same thought, although voyage is 32k vs 128k for cohere 4.

Anecdotal evidence points to benchmarks correlating with result quality for data I've dealt with. I haven't spent a lot of time comparing results between models, because we were happy with the results after trying a few and tuning some settings.

Unless my dataset lines up really well with a benchmark's dataset, creating my own benchmark is probably the only way to know which model is "best".