All the medium speed stuff I see (not 64Gb Serdes or even Thunderbolt) is differential current drive/receive though they may be voltage limited on the output. T

All the medium speed stuff I see (not 64Gb Serdes or even Thunderbolt) is differential current drive/receive though they may be voltage limited on the output. Those still seem to be designed as 50ohm, but they have some fairly high resistance connection's. Even at 1Gb getting a clean eye requires lots of equalization and careful routing, if you want to go 10+ inches.