> I've not yet seen a study that shows that virtual threads offer a huge benefit.

Not exactly Java virtual threads, but a study on how userland threads beat kernel threads.

https://cs.uwaterloo.ca/~mkarsten/papers/sigmetrics2020.html

For quick results, check figures 11 and 15 from the (preprint) paper. Userland threads ("fred") have ~50% higher throughput while having orders of magnitude better latency at high load levels, in a real-world application (memcached).