This one: https://www.fs.com/products/133619.html
It’s confirmed working at 2.5Gbps on a few devices. (BCM57810S, Ubiquity ES-16-XG…)
One interface locked at 2.5Gbps is perfectly fine as long as another one runs at 10Gbps.
Something like bl2_qspi_xg1_2.5g.pbl