Very poor connection: fluctuating ping up to ~1000ms, weak transfer rate and short occasional lock-ups (which didn't happened with other cards i tested). It could be hardware failure or malfunctioning driver, but even then it's still funtional.

lspci -vvnnk

03:02.0 Ethernet controller [0200]: Macronix, Inc. [MXIC] MX987x5 [10d9:0531] (rev 25)
        Subsystem: Macronix, Inc. [MXIC] MX987x5 [10d9:0531]
        Control: I/O+ Mem+ BusMaster+ SpecCycle- MemWINV- VGASnoop- ParErr- Stepping+ SERR- FastB2B- DisINTx-
        Status: Cap+ 66MHz- UDF- FastB2B+ ParErr- DEVSEL=medium >TAbort- <TAbort- <MAbort- >SERR- <PERR- INTx-
        Latency: 32 (2000ns min, 14000ns max), Cache Line Size: 32 bytes
        Interrupt: pin A routed to IRQ 23
        Region 0: I/O ports at e800 [size=256]
        Region 1: Memory at febffc00 (32-bit, non-prefetchable) [size=256]
        Expansion ROM at feb80000 [disabled] [size=256K]
        Capabilities: [44] Power Management version 1
                Flags: PMEClk- DSI- D1+ D2+ AuxCurrent=0mA PME(D0-,D1+,D2+,D3hot+,D3cold+)
                Status: D0 NoSoftRst- PME-Enable- DSel=0 DScale=0 PME-
        Kernel driver in use: tulip
        Kernel modules: tulip