[mwpmaybe]

I've started buying E810s even for 10G links. PCIe Gen4, lower power draw, RDMA support, generally backward-compatible with SFP+ DACs and transceivers, and relatively inexpensive. Not nearly as dirt-cheap as the X520s but not crazy expensive (last I looked, at least). As I gradually replace switches over the next few years I can start taking advantage of 25G.

[theatrus2]

This is the way. The 10G cards are ancient and hog all the PCIe lanes.

I’ve had the best luck with Mellanox ConnectX 4 or 5 cards. The 5 can happily run 25G on a modern lane constrained system.

[erincandescent]

I've seen lots of pretty terrible experiences with the i40e and newer Intel drivers.

For newer NICs than the X520s I'd probably grab a Connect-X card.

[mwpmaybe]

They've been stable for me but I'd be lying if I said I'd only heard good things.

Looks like prices on the E810-XXVDA2 have come up since the last time I looked while prices on the ConnectX-6 Lx have come down, so that'd be a good option!