Looking for high-speed serial protocol (FPGA implementation)

I've found that my vendor has a 4-wire RS-485 full-duplex connection into an FPGA fast enough to handle 5-10 Mbits, and I'd like to coordinate communication using that interface (together with some isolators). What would be a good protocol for exchanging packets of 4-20 32-bit words, with acknowledges? I need to exchange simple command/reply sequences, receive asynchronous events, and send/receive bulk data (firmware updates, realtime sensor data). I figure something with embedded clock and data over 2 wires is needed, but don't know what options are available. 10 Mbit Ethernet and HDLC come to mind, though. Multi-drop would be a plus, with devices wired in a daisy chain. On the host side I want to use a tiny Linux card, so a protocol with good hardware support in SBCs would be nice.