FIX and WebSockets in almost all cases have the same latency/execution speed. In some circumstances FIX might be insignificantly faster, via bypassing the processing queue and therefore cancelling orders faster. FIX is directly routed, not built on top of websocket, however it is more limited in features.
REST is slightly slower because each request is pre-processed on connection (since as opposed to WS and FIX, REST requests don’t queue) and then sent to the currency worker.
Most connections to the Deribit server can be classified as being colocated or external. Naturally, due to the lower distance to our server, colocated connections and VPS connections will have a faster RTT than external connections.
RTT: The round trip time from your machine to our matching engine and back again.
Additionally, external connections are filtered through our loadbalancer(s) for internet based connections. This could be considered an extra ‘hop’ for connectivity and will add 10-20 microseconds for processing and filtering, in addition to any latency for global connection distance from our server location in London, LD4 data centre.