Is Wifi With Arduino Fast Enough to Control a Vehicle?
Yes, this IS possible. There are even people who control their Quadrocopters with WiFi, but the latency really is a problem.
this thing is a commercial product and they let the user control it with wifi, but they have a huge load on algorithms on board to make it controllable.
in your application I would never use WiFi but 433MHz/868MHz you can buy modules for around 5€ - called RFM12 (from hoperf). there is a huge load of librarys for these in the internet.
Small tip: don't do all the processing on the one big host, the delay takes longer than the processing on board.